Commit 8eeee4e2 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

send_sigio_to_task: sanitize the usage of fown->signum 



send_sigio_to_task() reads fown->signum several times, we can race with
F_SETSIG which changes ->signum lockless.  In theory, this can fool
security checks or we can call group_send_sig_info() with the wrong
->si_signo which does not match "int sig".

Change the code to cache ->signum.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f83b1e61

fs/fcntl.c

+11 −5
Original line number Diff line number Diff line
@@ -432,10 +432,16 @@ static void send_sigio_to_task(struct task_struct *p, 
			       int fd,

			       int reason)

{

	if (!sigio_perm(p, fown, fown->signum))

	/*

	 * F_SETSIG can change ->signum lockless in parallel, make

	 * sure we read it once and use the same value throughout.

	 */

	int signum = ACCESS_ONCE(fown->signum);



	if (!sigio_perm(p, fown, signum))

		return;



	switch (fown->signum) {

	switch (signum) {

		siginfo_t si;

		default:

			/* Queue a rt signal with the appropriate fd as its
@@ -444,7 +450,7 @@ static void send_sigio_to_task(struct task_struct *p, 
			   delivered even if we can't queue.  Failure to

			   queue in this case _should_ be reported; we fall

			   back to SIGIO in that case. --sct */

			si.si_signo = fown->signum;

			si.si_signo = signum;

			si.si_errno = 0;

		        si.si_code  = reason;

			/* Make sure we are called with one of the POLL_*
@@ -456,7 +462,7 @@ static void send_sigio_to_task(struct task_struct *p, 
			else

				si.si_band = band_table[reason - POLL_IN];

			si.si_fd    = fd;

			if (!group_send_sig_info(fown->signum, &si, p))

			if (!group_send_sig_info(signum, &si, p))

				break;

		/* fall-through: fall back on the old plain SIGIO signal */

		case 0:

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