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

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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@quobyte.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: bcba24ccdc ("fuse: enable asynchronous processing direct IO")
Cc: <stable@vger.kernel.org> # 3.10+
This commit is contained in:
Robert Doebbelin 2016-03-07 09:50:56 +01:00 committed by Miklos Szeredi
parent b562e44f50
commit 7cabc61e01
1 changed files with 4 additions and 3 deletions
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7
fs/fuse/file.c
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@ -2843,6 +2843,7 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter, loff_t offset)
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, struct iov_iter *iter, loff_t offset)
* 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, struct iov_iter *iter, loff_t offset)
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);