[PATCH 3.16 074/328] fuse: Don't access pipe->buffers without pipe_lock()

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>

commit a2477b0e67c52f4364a47c3ad70902bc2a61bd4c upstream.

fuse_dev_splice_write() reads pipe->buffers to determine the size of
'bufs' array before taking the pipe_lock(). This is not safe as
another thread might change the 'pipe->buffers' between the allocation
and taking the pipe_lock(). So we end up with too small 'bufs' array.

Move the bufs allocations inside pipe_lock()/pipe_unlock() to fix this.

Fixes: dd3bb14f44a6 ("fuse: support splice() writing to fuse device")
Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/fuse/dev.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1913,11 +1913,14 @@ static ssize_t fuse_dev_splice_write(str
 	if (!fc)
 		return -EPERM;
 
+	pipe_lock(pipe);
+
 	bufs = kmalloc(pipe->buffers * sizeof(struct pipe_buffer), GFP_KERNEL);
-	if (!bufs)
+	if (!bufs) {
+		pipe_unlock(pipe);
 		return -ENOMEM;
+	}
 
-	pipe_lock(pipe);
 	nbuf = 0;
 	rem = 0;
 	for (idx = 0; idx < pipe->nrbufs && rem < len; idx++)