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

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Message-Id: <20180717160035.9422-1-aryabinin@virtuozzo.com>
Date:   Tue, 17 Jul 2018 19:00:33 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        stable@...r.kernel.org
Subject: [PATCH v2 1/3] fs/fuse, splice_write: Don't access pipe->buffers without pipe_lock()

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@...tuozzo.com>
Cc: <stable@...r.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