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From:   Dominique Martinet <asmadeus@codewreck.org>
Date:   Wed, 03 May 2023 16:49:26 +0900
Subject: [PATCH v2 2/5] 9p: virtio: fix unlikely null pointer deref in
 handle_rerror
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Message-Id: <20230427-scan-build-v2-2-bb96a6e6a33b@codewreck.org>
References: <20230427-scan-build-v2-0-bb96a6e6a33b@codewreck.org>
In-Reply-To: <20230427-scan-build-v2-0-bb96a6e6a33b@codewreck.org>
To:     Eric Van Hensbergen <ericvh@gmail.com>,
        Latchesar Ionkov <lucho@ionkov.net>,
        Christian Schoenebeck <linux_oss@crudebyte.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     Simon Horman <simon.horman@corigine.com>, v9fs@lists.linux.dev,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        Dominique Martinet <asmadeus@codewreck.org>
Precedence: bulk

handle_rerror can dereference the pages pointer, but it is not
necessarily set for small payloads.
In practice these should be filtered out by the size check, but
might as well double-check explicitly.

This fixes the following scan-build warnings:
net/9p/trans_virtio.c:401:24: warning: Dereference of null pointer [core.NullDereference]
                memcpy_from_page(to, *pages++, offs, n);
                                     ^~~~~~~~
net/9p/trans_virtio.c:406:23: warning: Dereference of null pointer (loaded from variable 'pages') [core.NullDereference]
        memcpy_from_page(to, *pages, offs, size);
                             ^~~~~~

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
---
 net/9p/trans_virtio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 3c27ffb781e3..2c9495ccda6b 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -384,7 +384,7 @@ static void handle_rerror(struct p9_req_t *req, int in_hdr_len,
 	void *to = req->rc.sdata + in_hdr_len;
 
 	// Fits entirely into the static data?  Nothing to do.
-	if (req->rc.size < in_hdr_len)
+	if (req->rc.size < in_hdr_len || !pages)
 		return;
 
 	// Really long error message?  Tough, truncate the reply.  Might get

-- 
2.39.2