Fix a race condition in FASYNC handling

Changeset a238b79 (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]>
adn770 · Dec 5, 2008 · 218d11a · 218d11a
1 parent f2f1fa7
commit 218d11a
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Showing 2 changed files with 15 additions and 4 deletions.
diff --git 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 * 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;
 }
 

diff --git a/fs/ioctl.c b/fs/ioctl.c
@@ -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: