Commit 218d11a8 authored by Jonathan Corbet's avatar Jonathan Corbet Committed by Linus Torvalds
Browse files

Fix a race condition in FASYNC handling 



Changeset a238b790 (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: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f2f1fa78

fs/fcntl.c

+7 −0
Original line number Diff line number Diff line
@@ -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;

}

fs/ioctl.c

+8 −4
Original line number Diff line number Diff line
@@ -400,11 +400,9 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp, 


	/* 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)
@@ -440,11 +438,17 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd, 
		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;



	case FIOQSIZE:

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