[PATCH v2 1/3] fs/fuse, splice_write: Don't access pipe->buffers without pipe_lock()

[Andrey Ryabinin]

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 <aryabi...@virtuozzo.com>
Cc: <sta...@vger.kernel.org>
---
 fs/fuse/dev.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index c6b88fa85e2e..702592cce546 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1944,12 +1944,15 @@ static ssize_t fuse_dev_splice_write(struct 
pipe_inode_info *pipe,
        if (!fud)
                return -EPERM;
 
+       pipe_lock(pipe);
+
        bufs = kmalloc_array(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++)
-- 
2.16.4