Date: Sun, 27 Dec 1998 20:40:32 +0100 From: Andrea Arcangeli <andrea@E-MIND.COM> Subject: [patch] fix for urandom read(2) not interruptible To: BUGTRAQ@NETSPACE.ORG After having read phrak54 about Linux /dev/u?random (and this is the reason I am CCing also to bugtraq ;), I was playing a bit with the random driver it and I noticed that was difficult to kill `dd if=/dev/urandom of=/dev/null bs=100000k count=20000' once started ;)). The machine was eavily loaded and the process was unkillable and I the fastest thing to restore the system is been a reset... It's a bug in random.c that doesn' t check for signal pending inside the read(2) code, so you have no chance to kill the process via signals until the read(2) syscall is finished, and it could take a lot of time before return, if the buffer given to the read syscall is very big... Here the fix against 2.1.132: Index: linux/drivers/char/random.c diff -u linux/drivers/char/random.c:1.1.1.1 linux/drivers/char/random.c:1.1.1.1.2.3 --- linux/drivers/char/random.c:1.1.1.1 Fri Nov 20 00:02:25 1998 +++ linux/drivers/char/random.c Sun Dec 27 20:19:16 1998 @@ -232,6 +232,11 @@ * Eastlake, Steve Crocker, and Jeff Schiller. */ +/* + * Added a check for signal pending in the extract_entropy() loop to allow + * the read(2) syscall to be interrupted. Copyright (C) 1998 Andrea Arcangeli + */ + #include <linux/utsname.h> #include <linux/config.h> #include <linux/kernel.h> @@ -1269,7 +1274,14 @@ buf += i; add_timer_randomness(r, &extract_timer_state, nbytes); if (to_user && current->need_resched) + { + if (signal_pending(current)) + { + ret = -EINTR; + break; + } schedule(); + } } /* Wipe data just returned from memory */ And here a fix against 2.0.36: --- linux/drivers/char/random.c.orig Sun Dec 27 20:22:53 1998 +++ linux/drivers/char/random.c Sun Dec 27 20:24:17 1998 @@ -226,6 +226,11 @@ * Eastlake, Steve Crocker, and Jeff Schiller. */ +/* + * Added a check for signal pending in the extract_entropy() loop to allow + * the read(2) syscall to be interrupted. Copyright (C) 1998 Andrea Arcangeli + */ + #include <linux/config.h> /* CONFIG_RST_COOKIES and CONFIG_SYN_COOKIES */ #include <linux/utsname.h> #include <linux/kernel.h> @@ -1004,7 +1009,14 @@ buf += i; add_timer_randomness(r, &extract_timer_state, nbytes); if (to_user && need_resched) + { + if (signal_pending(current)) + { + ret = -EINTR; + break; + } schedule(); + } } /* Wipe data from memory */ Andrea Arcangeli