| Message ID | 20240220122156.43131-1-tparkin@katalix.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 359e54a93ab43d32ee1bff3c2f9f10cb9f6b6e79 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net] l2tp: pass correct message length to ip6_append_data | expand |
On Tue, Feb 20, 2024 at 12:21:56PM +0000, Tom Parkin wrote: > l2tp_ip6_sendmsg needs to avoid accounting for the transport header > twice when splicing more data into an already partially-occupied skbuff. > > To manage this, we check whether the skbuff contains data using > skb_queue_empty when deciding how much data to append using > ip6_append_data. > > However, the code which performed the calculation was incorrect: > > ulen = len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0; > > ...due to C operator precedence, this ends up setting ulen to > transhdrlen for messages with a non-zero length, which results in > corrupted packets on the wire. > > Add parentheses to correct the calculation in line with the original > intent. > > Fixes: 9d4c75800f61 ("ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data()") > Cc: David Howells <dhowells@redhat.com> > Cc: stable@vger.kernel.org > Signed-off-by: Tom Parkin <tparkin@katalix.com> Reviewed-by: Simon Horman <horms@kernel.org> > --- > This issue was uncovered by Debian build-testing for the > golang-github-katalix-go-l2tp package[1]. > > It seems 9d4c75800f61 has been backported to the linux-6.1.y stable > kernel (and possibly others), so I think this fix will also need > backporting. > > The bug is currently seen on at least Debian Bookworm, Ubuntu Jammy, and > Debian testing/unstable. In that case perhaps this is appropriate - citing the patch that 9d4c75800f61 tried to fix? Fixes: a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6") > > Unfortunately tests using "ip l2tp" and which focus on dataplane > transport will not uncover this bug: it's necessary to send a packet > using an L2TPIP6 socket opened by userspace, and to verify the packet on > the wire. The l2tp-ktest[2] test suite has been extended to cover this. > > [1]. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1063746 > [2]. https://github.com/katalix/l2tp-ktest ...
Hello: This patch was applied to netdev/net.git (main) by Paolo Abeni <pabeni@redhat.com>: On Tue, 20 Feb 2024 12:21:56 +0000 you wrote: > l2tp_ip6_sendmsg needs to avoid accounting for the transport header > twice when splicing more data into an already partially-occupied skbuff. > > To manage this, we check whether the skbuff contains data using > skb_queue_empty when deciding how much data to append using > ip6_append_data. > > [...] Here is the summary with links: - [net] l2tp: pass correct message length to ip6_append_data https://git.kernel.org/netdev/net/c/359e54a93ab4 You are awesome, thank you!
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c index dd3153966173..7bf14cf9ffaa 100644 --- a/net/l2tp/l2tp_ip6.c +++ b/net/l2tp/l2tp_ip6.c @@ -627,7 +627,7 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) back_from_confirm: lock_sock(sk); - ulen = len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0; + ulen = len + (skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0); err = ip6_append_data(sk, ip_generic_getfrag, msg, ulen, transhdrlen, &ipc6, &fl6, (struct rt6_info *)dst,
l2tp_ip6_sendmsg needs to avoid accounting for the transport header twice when splicing more data into an already partially-occupied skbuff. To manage this, we check whether the skbuff contains data using skb_queue_empty when deciding how much data to append using ip6_append_data. However, the code which performed the calculation was incorrect: ulen = len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0; ...due to C operator precedence, this ends up setting ulen to transhdrlen for messages with a non-zero length, which results in corrupted packets on the wire. Add parentheses to correct the calculation in line with the original intent. Fixes: 9d4c75800f61 ("ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data()") Cc: David Howells <dhowells@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Tom Parkin <tparkin@katalix.com> --- This issue was uncovered by Debian build-testing for the golang-github-katalix-go-l2tp package[1]. It seems 9d4c75800f61 has been backported to the linux-6.1.y stable kernel (and possibly others), so I think this fix will also need backporting. The bug is currently seen on at least Debian Bookworm, Ubuntu Jammy, and Debian testing/unstable. Unfortunately tests using "ip l2tp" and which focus on dataplane transport will not uncover this bug: it's necessary to send a packet using an L2TPIP6 socket opened by userspace, and to verify the packet on the wire. The l2tp-ktest[2] test suite has been extended to cover this. [1]. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1063746 [2]. https://github.com/katalix/l2tp-ktest --- net/l2tp/l2tp_ip6.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)