Mainline commit 89c22d8c3b27 ("net: Fix skb csum races when peeking")
backport into pre-3.19 stable kernels introduces a regression causing
null pointer dererefence in skb_copy_and_csum_datagram_iovec().
This commit only sets CHECKSUM_UNNECESSARY for non-shared skb, allowing
udp_recvmsg() to take the "else" branch of if (skb_csum_unnecessary(skb))
when called with null iovec (and len=0, e.g. when peeking for datagram
size first). The problem is that unlike skb_copy_and_csum_datagram_msg()
called in this path since 3.19, skb_copy_and_csum_datagram_iovec() does
not handle null iov parameter and always dereferences iov->iov_len. This
is especially harmful when udp_recvmsg() is called in kernel context,
e.g. from kernel nfsd.
Band-aid skb_copy_and_csum_datagram_iovec() by testing iov for null and
only checking the checksum in this case.
Signed-off-by: Michal Kubecek <mkubecek@xxxxxxx>
---
net/core/datagram.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 3a402a7b20e9..f8b38794fa9b 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -799,6 +799,13 @@ int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
if (!chunk)
return 0;
+ if (!iov) {
+ if (__skb_checksum_complete(skb))
+ goto csum_error;
+ else
+ return 0;
+ }
+
/* Skip filled elements.
* Pretty silly, look at memcpy_toiovec, though 8)
*/
--
2.6.2
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