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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Miklos Szeredi <mszeredi@redhat.com>
Subject: [PATCH 4.18 058/123] fuse: Dont access pipe->buffers without pipe_lock()
Date:   Mon,  3 Sep 2018 18:56:42 +0200
Message-Id: <20180903165721.893005227@linuxfoundation.org>
In-Reply-To: <20180903165719.499675257@linuxfoundation.org>
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4.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Andrey Ryabinin <aryabinin@virtuozzo.com>

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@virtuozzo.com>
Cc: <stable@vger.kernel.org> # v2.6.35
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/fuse/dev.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1944,12 +1944,15 @@ static ssize_t fuse_dev_splice_write(str
 	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++)