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Fix a race condition in FASYNC handling

Browse source 
Changeset a238b790d5 (Call fasync()
functions without the BKL) introduced a race which could leave
file->f_flags in a state inconsistent with what the underlying
driver/filesystem believes.  Revert that change, and also fix the same
races in ioctl_fioasync() and ioctl_fionbio().

This is a minimal, short-term fix; the real fix will not involve the
BKL.

Reported-by: Oleg Nesterov <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Al Viro <[email protected]>
Cc: [email protected]
Signed-off-by: Jonathan Corbet <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Jonathan Corbet 2008-12-05 16:12:48 -07:00 • committed by Linus Torvalds
commit 218d11a8b0
2 changed files with 15 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

7
fs/fcntl.c
View file

@ -19,6 +19,7 @@
#include <linux/signal.h>
#include <linux/rcupdate.h>
#include <linux/pid_namespace.h>
#include <linux/smp_lock.h>
#include <asm/poll.h>
#include <asm/siginfo.h>
@ -175,6 +176,11 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
if (error)
return error;
/*
* We still need a lock here for now to keep multiple FASYNC calls
* from racing with each other.
*/
lock_kernel();
if ((arg ^ filp->f_flags) & FASYNC) {
if (filp->f_op && filp->f_op->fasync) {
error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0);
@ -185,6 +191,7 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
out:
unlock_kernel();
return error;
}