Linux Security Module Development¶

Based on https://lore.kernel.org/r/20071026073721.618b4778@laptopd505.fenrus.org, a new LSM is accepted into the kernel when its intent (a description of what it tries to protect against and in what cases one would expect to use it) has been appropriately documented in Documentation/admin-guide/LSM/. This allows an LSM’s code to be easily compared to its goals, and so that end users and distros can make a more informed decision about which LSMs suit their requirements.

For extensive documentation on the available LSM hook interfaces, please see security/security.c and associated structures:

void security_free_mnt_opts(void **mnt_opts)¶: Free memory associated with mount options

Parameters

void **mnt_opts: LSM processed mount options

Description

Free memory associated with mnt_ops.

int security_sb_eat_lsm_opts(char *options, void **mnt_opts)¶: Consume LSM mount options

Parameters

char *options: mount options
void **mnt_opts: LSM processed mount options

Description

Eat (scan options) and save them in mnt_opts.

Return

Returns 0 on success, negative values on failure.

int security_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts)¶: Check if new mount options are allowed

Parameters

struct super_block *sb: filesystem superblock
void *mnt_opts: new mount options

Description

Determine if the new mount options in mnt_opts are allowed given the existing mounted filesystem at sb. sb superblock being compared.

Return

Returns 0 if options are compatible.

int security_sb_remount(struct super_block *sb, void *mnt_opts)¶: Verify no incompatible mount changes during remount

Parameters

struct super_block *sb: filesystem superblock
void *mnt_opts: (re)mount options

Description

Extracts security system specific mount options and verifies no changes are being made to those options.

Return

Returns 0 if permission is granted.

int security_sb_set_mnt_opts(struct super_block *sb, void *mnt_opts, unsigned long kern_flags, unsigned long *set_kern_flags)¶: Set the mount options for a filesystem

Parameters

struct super_block *sb: filesystem superblock
void *mnt_opts: binary mount options
unsigned long kern_flags: kernel flags (in)
unsigned long *set_kern_flags: kernel flags (out)

Description

Set the security relevant mount options used for a superblock.

Return

Returns 0 on success, error on failure.

int security_sb_clone_mnt_opts(const struct super_block *oldsb, struct super_block *newsb, unsigned long kern_flags, unsigned long *set_kern_flags)¶: Duplicate superblock mount options

Parameters

const struct super_block *oldsb: source superblock
struct super_block *newsb: destination superblock
unsigned long kern_flags: kernel flags (in)
unsigned long *set_kern_flags: kernel flags (out)

Description

Copy all security options from a given superblock to another.

Return

Returns 0 on success, error on failure.

int security_dentry_init_security(struct dentry *dentry, int mode, const struct qstr *name, const char **xattr_name, void **ctx, u32 *ctxlen)¶: Perform dentry initialization

Parameters

struct dentry *dentry: the dentry to initialize
int mode: mode used to determine resource type
const struct qstr *name: name of the last path component
const char **xattr_name: name of the security/LSM xattr
void **ctx: pointer to the resulting LSM context
u32 *ctxlen: length of ctx

Description

Compute a context for a dentry as the inode is not yet available since NFSv4 has no label backed by an EA anyway. It is important to note that xattr_name does not need to be free’d by the caller, it is a static string.

Return

Returns 0 on success, negative values on failure.

int security_dentry_create_files_as(struct dentry *dentry, int mode, struct qstr *name, const struct cred *old, struct cred *new)¶: Perform dentry initialization

Parameters

struct dentry *dentry: the dentry to initialize
int mode: mode used to determine resource type
struct qstr *name: name of the last path component
const struct cred *old: creds to use for LSM context calculations
struct cred *new: creds to modify

Description

Compute a context for a dentry as the inode is not yet available and set that context in passed in creds so that new files are created using that context. Context is calculated using the passed in creds and not the creds of the caller.

Return

Returns 0 on success, error on failure.

int security_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, const initxattrs initxattrs, void *fs_data)¶: Initialize an inode’s LSM context

Parameters

struct inode *inode: the inode
struct inode *dir: parent directory
const struct qstr *qstr: last component of the pathname
const initxattrs initxattrs: callback function to write xattrs
void *fs_data: filesystem specific data

Description

Obtain the security attribute name suffix and value to set on a newly created inode and set up the incore security field for the new inode. This hook is called by the fs code as part of the inode creation transaction and provides for atomic labeling of the inode, unlike the post_create/mkdir/... hooks called by the VFS.

The hook function is expected to populate the xattrs array, by calling lsm_get_xattr_slot() to retrieve the slots reserved by the security module with the lbs_xattr_count field of the lsm_blob_sizes structure. For each slot, the hook function should set ->name to the attribute name suffix (e.g. selinux), to allocate ->value (will be freed by the caller) and set it to the attribute value, to set ->value_len to the length of the value. If the security module does not use security attributes or does not wish to put a security attribute on this particular inode, then it should return -EOPNOTSUPP to skip this processing.

Return

Returns 0 if the LSM successfully initialized all of the inode: security attributes that are required, negative values otherwise.

int security_path_mknod(const struct path *dir, struct dentry *dentry, umode_t mode, unsigned int dev)¶: Check if creating a special file is allowed

Parameters

const struct path *dir: parent directory
struct dentry *dentry: new file
umode_t mode: new file mode
unsigned int dev: device number

Description

Check permissions when creating a file. Note that this hook is called even if mknod operation is being done for a regular file.

Return

Returns 0 if permission is granted.

int security_path_mkdir(const struct path *dir, struct dentry *dentry, umode_t mode)¶: Check if creating a new directory is allowed

Parameters

const struct path *dir: parent directory
struct dentry *dentry: new directory
umode_t mode: new directory mode

Description

Check permissions to create a new directory in the existing directory.

Return

Returns 0 if permission is granted.

int security_path_unlink(const struct path *dir, struct dentry *dentry)¶: Check if removing a hard link is allowed

Parameters

const struct path *dir: parent directory
struct dentry *dentry: file

Description

Check the permission to remove a hard link to a file.

Return

Returns 0 if permission is granted.

int security_path_rename(const struct path *old_dir, struct dentry *old_dentry, const struct path *new_dir, struct dentry *new_dentry, unsigned int flags)¶: Check if renaming a file is allowed

Parameters

const struct path *old_dir: parent directory of the old file
struct dentry *old_dentry: the old file
const struct path *new_dir: parent directory of the new file
struct dentry *new_dentry: the new file
unsigned int flags: flags

Description

Check for permission to rename a file or directory.

Return

Returns 0 if permission is granted.

int security_inode_create(struct inode *dir, struct dentry *dentry, umode_t mode)¶: Check if creating a file is allowed

Parameters

struct inode *dir: the parent directory
struct dentry *dentry: the file being created
umode_t mode: requested file mode

Description

Check permission to create a regular file.

Return

Returns 0 if permission is granted.

int security_inode_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)¶: Check if creation a new director is allowed

Parameters

struct inode *dir: parent directory
struct dentry *dentry: new directory
umode_t mode: new directory mode

Description

Check permissions to create a new directory in the existing directory associated with inode structure dir.

Return

Returns 0 if permission is granted.

int security_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry, struct iattr *attr)¶: Check if setting file attributes is allowed

Parameters

struct mnt_idmap *idmap: idmap of the mount
struct dentry *dentry: file
struct iattr *attr: new attributes

Description

Check permission before setting file attributes. Note that the kernel call to notify_change is performed from several locations, whenever file attributes change (such as when a file is truncated, chown/chmod operations, transferring disk quotas, etc).

Return

Returns 0 if permission is granted.

int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size)¶: List the xattr security label names

Parameters

struct inode *inode: inode
char *buffer: buffer
size_t buffer_size: size of buffer

Description

Copy the extended attribute names for the security labels associated with inode into buffer. The maximum size of buffer is specified by buffer_size. buffer may be NULL to request the size of the buffer required.

Return

Returns number of bytes used/required on success.

int security_inode_copy_up(struct dentry *src, struct cred **new)¶: Create new creds for an overlayfs copy-up op

Parameters

struct dentry *src: union dentry of copy-up file
struct cred **new: newly created creds

Description

A file is about to be copied up from lower layer to upper layer of overlay filesystem. Security module can prepare a set of new creds and modify as need be and return new creds. Caller will switch to new creds temporarily to create new file and release newly allocated creds.

Return

Returns 0 on success or a negative error code on error.

int security_inode_copy_up_xattr(struct dentry *src, const char *name)¶: Filter xattrs in an overlayfs copy-up op

Parameters

struct dentry *src: union dentry of copy-up file
const char *name: xattr name

Description

Filter the xattrs being copied up when a unioned file is copied up from a lower layer to the union/overlay layer. The caller is responsible for reading and writing the xattrs, this hook is merely a filter.

Return

Returns 0 to accept the xattr, -ECANCELED to discard the xattr,: -EOPNOTSUPP if the security module does not know about attribute, or a negative error code to abort the copy up.

int security_inode_setintegrity(const struct inode *inode, enum lsm_integrity_type type, const void *value, size_t size)¶: Set the inode’s integrity data

Parameters

const struct inode *inode: inode
enum lsm_integrity_type type: type of integrity, e.g. hash digest, signature, etc
const void *value: the integrity value
size_t size: size of the integrity value

Description

Register a verified integrity measurement of a inode with LSMs. LSMs should free the previously saved data if value is NULL.

Return

Returns 0 on success, negative values on failure.

int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)¶: Check if an ioctl is allowed

Parameters

struct file *file: associated file
unsigned int cmd: ioctl cmd
unsigned long arg: ioctl arguments

Description

Check permission for an ioctl operation on file. Note that arg sometimes represents a user space pointer; in other cases, it may be a simple integer value. When arg represents a user space pointer, it should never be used by the security module.

Return

Returns 0 if permission is granted.

int security_file_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg)¶: Check if an ioctl is allowed in compat mode

Parameters

struct file *file: associated file
unsigned int cmd: ioctl cmd
unsigned long arg: ioctl arguments

Description

Compat version of security_file_ioctl() that correctly handles 32-bit processes running on 64-bit kernels.

Return

Returns 0 if permission is granted.

int security_file_post_open(struct file *file, int mask)¶: Evaluate a file after it has been opened

Parameters

struct file *file: the file
int mask: access mask

Description

Evaluate an opened file and the access mask requested with open(). The hook is useful for LSMs that require the file content to be available in order to make decisions.

Return

Returns 0 if permission is granted.

void security_cred_getsecid(const struct cred *c, u32 *secid)¶: Get the secid from a set of credentials

Parameters

const struct cred *c: credentials
u32 *secid: secid value

Description

Retrieve the security identifier of the cred structure c. In case of failure, secid will be set to zero.

void security_cred_getlsmprop(const struct cred *c, struct lsm_prop *prop)¶: Get the LSM data from a set of credentials

Parameters

const struct cred *c: credentials
struct lsm_prop *prop: destination for the LSM data

Description

Retrieve the security data of the cred structure c. In case of failure, prop will be cleared.

int security_kernel_read_file(struct file *file, enum kernel_read_file_id id, bool contents)¶: Read a file specified by userspace

Parameters

struct file *file: file
enum kernel_read_file_id id: file identifier
bool contents: trust if security_kernel_post_read_file() will be called

Description

Read a file specified by userspace.

Return

Returns 0 if permission is granted.

int security_kernel_post_read_file(struct file *file, char *buf, loff_t size, enum kernel_read_file_id id)¶: Read a file specified by userspace

Parameters

struct file *file: file
char *buf: file contents
loff_t size: size of file contents
enum kernel_read_file_id id: file identifier

Description

Read a file specified by userspace. This must be paired with a prior call to security_kernel_read_file() call that indicated this hook would also be called, see security_kernel_read_file() for more information.

Return

Returns 0 if permission is granted.

int security_kernel_load_data(enum kernel_load_data_id id, bool contents)¶: Load data provided by userspace

Parameters

enum kernel_load_data_id id: data identifier
bool contents: true if security_kernel_post_load_data() will be called

Description

Load data provided by userspace.

Return

Returns 0 if permission is granted.

int security_kernel_post_load_data(char *buf, loff_t size, enum kernel_load_data_id id, char *description)¶: Load userspace data from a non-file source

Parameters

char *buf: data
loff_t size: size of data
enum kernel_load_data_id id: data identifier
char *description: text description of data, specific to the id value

Description

Load data provided by a non-file source (usually userspace buffer). This must be paired with a prior security_kernel_load_data() call that indicated this hook would also be called, see security_kernel_load_data() for more information.

Return

Returns 0 if permission is granted.

void security_current_getlsmprop_subj(struct lsm_prop *prop)¶: Current task’s subjective LSM data

Parameters

struct lsm_prop *prop: lsm specific information

Description

Retrieve the subjective security identifier of the current task and return it in prop.

void security_task_getlsmprop_obj(struct task_struct *p, struct lsm_prop *prop)¶: Get a task’s objective LSM data

Parameters

struct task_struct *p: target task
struct lsm_prop *prop: lsm specific information

Description

Retrieve the objective security identifier of the task_struct in p and return it in prop.

void security_d_instantiate(struct dentry *dentry, struct inode *inode)¶: Populate an inode’s LSM state based on a dentry

Parameters

struct dentry *dentry: dentry
struct inode *inode: inode

Description

Fill in inode security information for a dentry if allowed.

int security_ismaclabel(const char *name)¶: Check if the named attribute is a MAC label

Parameters

const char *name: full extended attribute name

Description

Check if the extended attribute specified by name represents a MAC label.

Return

Returns 1 if name is a MAC attribute otherwise returns 0.

int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)¶: Convert a secid to a secctx

Parameters

u32 secid: secid
char **secdata: secctx
u32 *seclen: secctx length

Description

Convert secid to security context. If secdata is NULL the length of the result will be returned in seclen, but no secdata will be returned. This does mean that the length could change between calls to check the length and the next call which actually allocates and returns the secdata.

Return

Return 0 on success, error on failure.

int security_lsmprop_to_secctx(struct lsm_prop *prop, char **secdata, u32 *seclen)¶: Convert a lsm_prop to a secctx

Parameters

struct lsm_prop *prop: lsm specific information
char **secdata: secctx
u32 *seclen: secctx length

Description

Convert a prop entry to security context. If secdata is NULL the length of the result will be returned in seclen, but no secdata will be returned. This does mean that the length could change between calls to check the length and the next call which actually allocates and returns the secdata.

Return

Return 0 on success, error on failure.

int security_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)¶: Convert a secctx to a secid

Parameters

const char *secdata: secctx
u32 seclen: length of secctx
u32 *secid: secid

Description

Convert security context to secid.

Return

Returns 0 on success, error on failure.

void security_release_secctx(char *secdata, u32 seclen)¶: Free a secctx buffer

Parameters

char *secdata: secctx
u32 seclen: length of secctx

Description

Release the security context.

void security_inode_invalidate_secctx(struct inode *inode)¶: Invalidate an inode’s security label

Parameters

struct inode *inode: inode

Description

Notify the security module that it must revalidate the security context of an inode.

int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen)¶: Notify the LSM of an inode’s security label

Parameters

struct inode *inode: inode
void *ctx: secctx
u32 ctxlen: length of secctx

Description

Notify the security module of what the security context of an inode should be. Initializes the incore security context managed by the security module for this inode. Example usage: NFS client invokes this hook to initialize the security context in its incore inode to the value provided by the server for the file when the server returned the file’s attributes to the client. Must be called with inode->i_mutex locked.

Return

Returns 0 on success, error on failure.

int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen)¶: Change the security label of an inode

Parameters

struct dentry *dentry: inode
void *ctx: secctx
u32 ctxlen: length of secctx

Description

Change the security context of an inode. Updates the incore security context managed by the security module and invokes the fs code as needed (via __vfs_setxattr_noperm) to update any backing xattrs that represent the context. Example usage: NFS server invokes this hook to change the security context in its incore inode and on the backing filesystem to a value provided by the client on a SETATTR operation. Must be called with inode->i_mutex locked.

Return

Returns 0 on success, error on failure.

int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)¶: Get the security label of an inode

Parameters

struct inode *inode: inode
void **ctx: secctx
u32 *ctxlen: length of secctx

Description

On success, returns 0 and fills out ctx and ctxlen with the security context for the given inode.

Return

Returns 0 on success, error on failure.

int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)¶: Check if a AF_UNIX stream is allowed

Parameters

struct sock *sock: originating sock
struct sock *other: peer sock
struct sock *newsk: new sock

Description

Check permissions before establishing a Unix domain stream connection between sock and other.

The unix_stream_connect and unix_may_send hooks were necessary because Linux provides an alternative to the conventional file name space for Unix domain sockets. Whereas binding and connecting to sockets in the file name space is mediated by the typical file permissions (and caught by the mknod and permission hooks in inode_security_ops), binding and connecting to sockets in the abstract name space is completely unmediated. Sufficient control of Unix domain sockets in the abstract name space isn’t possible using only the socket layer hooks, since we need to know the actual target socket, which is not looked up until we are inside the af_unix code.

Return

Returns 0 if permission is granted.

int security_unix_may_send(struct socket *sock, struct socket *other)¶: Check if AF_UNIX socket can send datagrams

Parameters

struct socket *sock: originating sock
struct socket *other: peer sock

Description

Check permissions before connecting or sending datagrams from sock to other.

The unix_stream_connect and unix_may_send hooks were necessary because Linux provides an alternative to the conventional file name space for Unix domain sockets. Whereas binding and connecting to sockets in the file name space is mediated by the typical file permissions (and caught by the mknod and permission hooks in inode_security_ops), binding and connecting to sockets in the abstract name space is completely unmediated. Sufficient control of Unix domain sockets in the abstract name space isn’t possible using only the socket layer hooks, since we need to know the actual target socket, which is not looked up until we are inside the af_unix code.

Return

Returns 0 if permission is granted.

int security_socket_socketpair(struct socket *socka, struct socket *sockb)¶: Check if creating a socketpair is allowed

Parameters

struct socket *socka: first socket
struct socket *sockb: second socket

Description

Check permissions before creating a fresh pair of sockets.

Return

Returns 0 if permission is granted and the connection was: established.

int security_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)¶: Check if an incoming network packet is allowed

Parameters

struct sock *sk: destination sock
struct sk_buff *skb: incoming packet

Description

Check permissions on incoming network packets. This hook is distinct from Netfilter’s IP input hooks since it is the first time that the incoming sk_buff skb has been associated with a particular socket, sk. Must not sleep inside this hook because some callers hold spinlocks.

Return

Returns 0 if permission is granted.

int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)¶: Get the remote peer label

Parameters

struct socket *sock: socket
struct sk_buff *skb: datagram packet
u32 *secid: remote peer label secid

Description

This hook allows the security module to provide peer socket security state for udp sockets on a per-packet basis to userspace via getsockopt SO_GETPEERSEC. The application must first have indicated the IP_PASSSEC option via getsockopt. It can then retrieve the security state returned by this hook for a packet via the SCM_SECURITY ancillary message type.

Return

Returns 0 on success, error on failure.

void security_sk_clone(const struct sock *sk, struct sock *newsk)¶: Clone a sock’s LSM state

Parameters

const struct sock *sk: original sock
struct sock *newsk: target sock

Description

Clone/copy security structure.

void security_sk_classify_flow(const struct sock *sk, struct flowi_common *flic)¶: Set a flow’s secid based on socket

Parameters

const struct sock *sk: original socket
struct flowi_common *flic: target flow

Description

Set the target flow’s secid to socket’s secid.

void security_req_classify_flow(const struct request_sock *req, struct flowi_common *flic)¶: Set a flow’s secid based on request_sock

Parameters

const struct request_sock *req: request_sock
struct flowi_common *flic: target flow

Description

Sets flic’s secid to req’s secid.

void security_sock_graft(struct sock *sk, struct socket *parent)¶: Reconcile LSM state when grafting a sock on a socket

Parameters

struct sock *sk: sock being grafted
struct socket *parent: target parent socket

Description

Sets parent’s inode secid to sk’s secid and update sk with any necessary LSM state from parent.

int security_inet_conn_request(const struct sock *sk, struct sk_buff *skb, struct request_sock *req)¶: Set request_sock state using incoming connect

Parameters

const struct sock *sk: parent listening sock
struct sk_buff *skb: incoming connection
struct request_sock *req: new request_sock

Description

Initialize the req LSM state based on sk and the incoming connect in skb.

Return

Returns 0 if permission is granted.

void security_inet_conn_established(struct sock *sk, struct sk_buff *skb)¶: Update sock’s LSM state with connection

Parameters

struct sock *sk: sock
struct sk_buff *skb: connection packet

Description

Update sock’s LSM state to represent a new connection from skb.

int security_secmark_relabel_packet(u32 secid)¶: Check if setting a secmark is allowed

Parameters

u32 secid: new secmark value

Description

Check if the process should be allowed to relabel packets to secid.

Return

Returns 0 if permission is granted.

void security_secmark_refcount_inc(void)¶: Increment the secmark labeling rule count

Parameters

void: no arguments

Description

Tells the LSM to increment the number of secmark labeling rules loaded.

void security_secmark_refcount_dec(void)¶: Decrement the secmark labeling rule count

Parameters

void: no arguments

Description

Tells the LSM to decrement the number of secmark labeling rules loaded.

int security_tun_dev_alloc_security(void **security)¶: Allocate a LSM blob for a TUN device

Parameters

void **security: pointer to the LSM blob

Description

This hook allows a module to allocate a security structure for a TUN device, returning the pointer in security.

Return

Returns a zero on success, negative values on failure.

void security_tun_dev_free_security(void *security)¶: Free a TUN device LSM blob

Parameters

void *security: LSM blob

Description

This hook allows a module to free the security structure for a TUN device.

int security_tun_dev_create(void)¶: Check if creating a TUN device is allowed

Parameters

void: no arguments

Description

Check permissions prior to creating a new TUN device.

Return

Returns 0 if permission is granted.

int security_tun_dev_attach_queue(void *security)¶: Check if attaching a TUN queue is allowed

Parameters

void *security: TUN device LSM blob

Description

Check permissions prior to attaching to a TUN device queue.

Return

Returns 0 if permission is granted.

int security_tun_dev_attach(struct sock *sk, void *security)¶: Update TUN device LSM state on attach

Parameters

struct sock *sk: associated sock
void *security: TUN device LSM blob

Description

This hook can be used by the module to update any security state associated with the TUN device’s sock structure.

Return

Returns 0 if permission is granted.

int security_tun_dev_open(void *security)¶: Update TUN device LSM state on open

Parameters

void *security: TUN device LSM blob

Description

This hook can be used by the module to update any security state associated with the TUN device’s security structure.

Return

Returns 0 if permission is granted.

int security_sctp_assoc_request(struct sctp_association *asoc, struct sk_buff *skb)¶: Update the LSM on a SCTP association req

Parameters

struct sctp_association *asoc: SCTP association
struct sk_buff *skb: packet requesting the association

Description

Passes the asoc and chunk->skb of the association INIT packet to the LSM.

Return

Returns 0 on success, error on failure.

int security_sctp_bind_connect(struct sock *sk, int optname, struct sockaddr *address, int addrlen)¶: Validate a list of addrs for a SCTP option

Parameters

struct sock *sk: socket
int optname: SCTP option to validate
struct sockaddr *address: list of IP addresses to validate
int addrlen: length of the address list

Description

Validiate permissions required for each address associated with sock sk. Depending on optname, the addresses will be treated as either a connect or bind service. The addrlen is calculated on each IPv4 and IPv6 address using sizeof(struct sockaddr_in) or sizeof(struct sockaddr_in6).

Return

Returns 0 on success, error on failure.

void security_sctp_sk_clone(struct sctp_association *asoc, struct sock *sk, struct sock *newsk)¶: Clone a SCTP sock’s LSM state

Parameters

struct sctp_association *asoc: SCTP association
struct sock *sk: original sock
struct sock *newsk: target sock

Description

Called whenever a new socket is created by accept(2) (i.e. a TCP style socket) or when a socket is ‘peeled off’ e.g userspace calls sctp_peeloff(3).

int security_sctp_assoc_established(struct sctp_association *asoc, struct sk_buff *skb)¶: Update LSM state when assoc established

Parameters

struct sctp_association *asoc: SCTP association
struct sk_buff *skb: packet establishing the association

Description

Passes the asoc and chunk->skb of the association COOKIE_ACK packet to the security module.

Return

Returns 0 if permission is granted.

int security_ib_pkey_access(void *sec, u64 subnet_prefix, u16 pkey)¶: Check if access to an IB pkey is allowed

Parameters

void *sec: LSM blob
u64 subnet_prefix: subnet prefix of the port
u16 pkey: IB pkey

Description

Check permission to access a pkey when modifying a QP.

Return

Returns 0 if permission is granted.

int security_ib_endport_manage_subnet(void *sec, const char *dev_name, u8 port_num)¶: Check if SMPs traffic is allowed

Parameters

void *sec: LSM blob
const char *dev_name: IB device name
u8 port_num: port number

Description

Check permissions to send and receive SMPs on a end port.

Return

Returns 0 if permission is granted.

int security_ib_alloc_security(void **sec)¶: Allocate an Infiniband LSM blob

Parameters

void **sec: LSM blob

Description

Allocate a security structure for Infiniband objects.

Return

Returns 0 on success, non-zero on failure.

void security_ib_free_security(void *sec)¶: Free an Infiniband LSM blob

Parameters

void *sec: LSM blob

Description

Deallocate an Infiniband security structure.

int security_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp, struct xfrm_user_sec_ctx *sec_ctx, gfp_t gfp)¶: Allocate a xfrm policy LSM blob

Parameters

struct xfrm_sec_ctx **ctxp: xfrm security context being added to the SPD
struct xfrm_user_sec_ctx *sec_ctx: security label provided by userspace
gfp_t gfp: gfp flags

Description

Allocate a security structure to the xp->security field; the security field is initialized to NULL when the xfrm_policy is allocated.

Return

Return 0 if operation was successful.

void security_xfrm_policy_free(struct xfrm_sec_ctx *ctx)¶: Free a xfrm security context

Parameters

struct xfrm_sec_ctx *ctx: xfrm security context

Description

Free LSM resources associated with ctx.

int security_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *sec_ctx)¶: Allocate a xfrm state LSM blob

Parameters

struct xfrm_state *x: xfrm state being added to the SAD
struct xfrm_user_sec_ctx *sec_ctx: security label provided by userspace

Description

Allocate a security structure to the x->security field; the security field is initialized to NULL when the xfrm_state is allocated. Set the context to correspond to sec_ctx.

Return

Return 0 if operation was successful.

int security_xfrm_state_delete(struct xfrm_state *x)¶: Check if deleting a xfrm state is allowed

Parameters

struct xfrm_state *x: xfrm state

Description

Authorize deletion of x->security.

Return

Returns 0 if permission is granted.

int security_locked_down(enum lockdown_reason what)¶: Check if a kernel feature is allowed

Parameters

enum lockdown_reason what: requested kernel feature

Description

Determine whether a kernel feature that potentially enables arbitrary code execution in kernel space should be permitted.

Return

Returns 0 if permission is granted.

int security_bdev_alloc(struct block_device *bdev)¶: Allocate a block device LSM blob

Parameters

struct block_device *bdev: block device

Description

Allocate and attach a security structure to bdev->bd_security. The security field is initialized to NULL when the bdev structure is allocated.

Return

Return 0 if operation was successful.

void security_bdev_free(struct block_device *bdev)¶: Free a block device’s LSM blob

Parameters

struct block_device *bdev: block device

Description

Deallocate the bdev security structure and set bdev->bd_security to NULL.

int security_bdev_setintegrity(struct block_device *bdev, enum lsm_integrity_type type, const void *value, size_t size)¶: Set the device’s integrity data

Parameters

struct block_device *bdev: block device
enum lsm_integrity_type type: type of integrity, e.g. hash digest, signature, etc
const void *value: the integrity value
size_t size: size of the integrity value

Description

Register a verified integrity measurement of a bdev with LSMs. LSMs should free the previously saved data if value is NULL. Please note that the new hook should be invoked every time the security information is updated to keep these data current. For example, in dm-verity, if the mapping table is reloaded and configured to use a different dm-verity target with a new roothash and signing information, the previously stored data in the LSM blob will become obsolete. It is crucial to re-invoke the hook to refresh these data and ensure they are up to date. This necessity arises from the design of device-mapper, where a device-mapper device is first created, and then targets are subsequently loaded into it. These targets can be modified multiple times during the device’s lifetime. Therefore, while the LSM blob is allocated during the creation of the block device, its actual contents are not initialized at this stage and can change substantially over time. This includes alterations from data that the LSMs ‘trusts’ to those they do not, making it essential to handle these changes correctly. Failure to address this dynamic aspect could potentially allow for bypassing LSM checks.

Return

Returns 0 on success, negative values on failure.

The Linux Kernel

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Linux Security Module Development¶