3.16.35-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Robert Doebbelin <robert@xxxxxxxxxxx>
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@xxxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Fixes: bcba24ccdc82 ("fuse: enable asynchronous processing direct IO")
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
fs/fuse/file.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2876,6 +2876,7 @@ fuse_direct_IO(int rw, struct kiocb *ioc
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;
@@ -2915,7 +2916,7 @@ fuse_direct_IO(int rw, struct kiocb *ioc
* 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)
@@ -2927,7 +2928,7 @@ fuse_direct_IO(int rw, struct kiocb *ioc
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);
--
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