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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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2009-06-17 00:27:10 +02:00 committed by Linus Torvalds
parent f83b1e616f
commit 8eeee4e2f0
1 changed files with 11 additions and 5 deletions
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16
fs/fcntl.c
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@ -428,14 +428,20 @@ static inline int sigio_perm(struct task_struct *p,
} }
static void send_sigio_to_task(struct task_struct *p, static void send_sigio_to_task(struct task_struct *p,
struct fown_struct *fown, struct fown_struct *fown,
int fd, int fd,
int reason) 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; return;
switch (fown->signum) { switch (signum) {
siginfo_t si; siginfo_t si;
default: default:
/* Queue a rt signal with the appropriate fd as its /* 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 delivered even if we can't queue. Failure to
queue in this case _should_ be reported; we fall queue in this case _should_ be reported; we fall
back to SIGIO in that case. --sct */ back to SIGIO in that case. --sct */
si.si_signo = fown->signum; si.si_signo = signum;
si.si_errno = 0; si.si_errno = 0;
si.si_code = reason; si.si_code = reason;
/* Make sure we are called with one of the POLL_* /* 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 else
si.si_band = band_table[reason - POLL_IN]; si.si_band = band_table[reason - POLL_IN];
si.si_fd = fd; si.si_fd = fd;
if (!group_send_sig_info(fown->signum, &si, p)) if (!group_send_sig_info(signum, &si, p))
break; break;
/* fall-through: fall back on the old plain SIGIO signal */ /* fall-through: fall back on the old plain SIGIO signal */
case 0: case 0: