[patch 14/83] Fix a race condition in FASYNC handling

Greg KH
2008-12-11T19:22:57Z

[-- Attachment #1: fix-a-race-condition-in-fasync-handling.patch --]
[-- Type: text/plain, Size: 2564 bytes --]

2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Jonathan Corbet <corbet@lwn.net>

commit 218d11a8b071b23b76c484fd5f72a4fe3306801e upstream.

Changeset a238b790d5f99c7832f9b73ac8847025815b85f7 (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 <oleg@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/fcntl.c | 7 +++++++
fs/ioctl.c | 12 ++++++++----
2 files changed, 15 insertions(+), 4 deletions(-)

--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -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 * f
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 * f

filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
out:
+ unlock_kernel();
return error;
}

--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -123,11 +123,9 @@ static int ioctl_fioasync(unsigned int f

/* Did FASYNC state change ? */
if ((flag ^ filp->f_flags) & FASYNC) {
- if (filp->f_op && filp->f_op->fasync) {
- lock_kernel();
+ if (filp->f_op && filp->f_op->fasync)
error = filp->f_op->fasync(fd, filp, on);
- unlock_kernel();
- } else
+ else
error = -ENOTTY;
}
if (error)
@@ -163,11 +161,17 @@ int do_vfs_ioctl(struct file *filp, unsi
break;

case FIONBIO:
+ /* BKL needed to avoid races tweaking f_flags */
+ lock_kernel();
error = ioctl_fionbio(filp, argp);
+ unlock_kernel();
break;

case FIOASYNC:
+ /* BKL needed to avoid races tweaking f_flags */
+ lock_kernel();
error = ioctl_fioasync(fd, filp, argp);
+ unlock_kernel();
break;