Patch "fuse: do not use iocb after it may have been freed" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

fuse: do not use iocb after it may have been freed

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fuse-do-not-use-iocb-after-it-may-have-been-freed.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Robert Doebbelin <[email protected]>
Date: Mon, 7 Mar 2016 09:50:56 +0100
Subject: fuse: do not use iocb after it may have been freed

From: Robert Doebbelin <[email protected]>

commit 7cabc61e01a0a8b663bd2b4c982aa53048218734 upstream.

There's a race in fuse_direct_IO(), whereby is_sync_kiocb() is called on an iocb that could have been freed if async io has already completed. The fix in this case is simple and obvious: cache the result before starting io.

It was discovered by KASan:

kernel: ==================================================================
kernel: BUG: KASan: use after free in fuse_direct_IO+0xb1a/0xcc0 at addr ffff88036c414390

---
 fs/fuse/file.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

@@ -2843,6 +2843,7 @@ fuse_direct_IO(struct kiocb *iocb, struc
 	loff_t i_size;
 	size_t count = iov_iter_count(iter);
 	struct fuse_io_priv *io;
+	bool is_sync = is_sync_kiocb(iocb);
 
 	pos = offset;
 	inode = file->f_mapping->host;

@@ -2882,11 +2883,11 @@ fuse_direct_IO(struct kiocb *iocb, struc
 	 * to wait on real async I/O requests, so we must submit this request
 	 * synchronously.
 	 */
-	if (!is_sync_kiocb(iocb) && (offset + count > i_size) &&
+	if (!is_sync && (offset + count > i_size) &&
 	    iov_iter_rw(iter) == WRITE)
 		io->async = false;
 
-	if (io->async && is_sync_kiocb(iocb))
+	if (io->async && is_sync)
 		io->done = &wait;
 
 	if (iov_iter_rw(iter) == WRITE) {

@@ -2900,7 +2901,7 @@ fuse_direct_IO(struct kiocb *iocb, struc
 		fuse_aio_complete(io, ret < 0 ? ret : 0, -1);
 
 		/* we have a non-extending, async request, so return */
-		if (!is_sync_kiocb(iocb))
+		if (!is_sync)
 			return -EIOCBQUEUED;
 
 		wait_for_completion(&wait);

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/fuse-do-not-use-iocb-after-it-may-have-been-freed.patch