linux-kernel - [PATCH 3.10 105/250] fuse: do not use iocb after it may have been freed

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Message-Id: <1496876436-32402-106-git-send-email-w@1wt.eu>
Date:   Thu,  8 Jun 2017 00:58:11 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Robert Doebbelin <robert@...byte.com>,
        Miklos Szeredi <mszeredi@...hat.com>, Jan Kara <jack@...e.cz>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 105/250] fuse: do not use iocb after it may have been freed

From: Robert Doebbelin <robert@...byte.com>

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

Signed-off-by: Robert Doebbelin <robert@...byte.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Fixes: bcba24ccdc82 ("fuse: enable asynchronous processing direct IO")
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Willy Tarreau <w@....eu>
---
 fs/fuse/file.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 35f604b..7ada0f0 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2398,6 +2398,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 	loff_t i_size;
 	size_t count = iov_length(iov, nr_segs);
 	struct fuse_io_priv *io;
+	bool is_sync = is_sync_kiocb(iocb);
 
 	pos = offset;
 	inode = file->f_mapping->host;
@@ -2433,7 +2434,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 	 * to wait on real async I/O requests, so we must submit this request
 	 * synchronously.
 	 */
-	if (!is_sync_kiocb(iocb) && (offset + count > i_size) && rw == WRITE)
+	if (!is_sync && (offset + count > i_size) && rw == WRITE)
 		io->async = false;
 
 	if (rw == WRITE)
@@ -2445,7 +2446,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 		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;
 
 		ret = wait_on_sync_kiocb(iocb);
-- 
2.8.0.rc2.1.gbe9624a