5.4-stable review patch. If anyone has any objections, please let me know.
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From: David Howells dhowells@redhat.com
[ Upstream commit 9d4c75800f61e5d75c1659ba201b6c0c7ead3070 ]
Including the transhdrlen in length is a problem when the packet is partially filled (e.g. something like send(MSG_MORE) happened previously) when appending to an IPv4 or IPv6 packet as we don't want to repeat the transport header or account for it twice. This can happen under some circumstances, such as splicing into an L2TP socket.
The symptom observed is a warning in __ip6_append_data():
WARNING: CPU: 1 PID: 5042 at net/ipv6/ip6_output.c:1800 __ip6_append_data.isra.0+0x1be8/0x47f0 net/ipv6/ip6_output.c:1800
that occurs when MSG_SPLICE_PAGES is used to append more data to an already partially occupied skbuff. The warning occurs when 'copy' is larger than the amount of data in the message iterator. This is because the requested length includes the transport header length when it shouldn't. This can be triggered by, for example:
sfd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_L2TP); bind(sfd, ...); // ::1 connect(sfd, ...); // ::1 port 7 send(sfd, buffer, 4100, MSG_MORE); sendfile(sfd, dfd, NULL, 1024);
Fix this by only adding transhdrlen into the length if the write queue is empty in l2tp_ip6_sendmsg(), analogously to how UDP does things.
l2tp_ip_sendmsg() looks like it won't suffer from this problem as it builds the UDP packet itself.
Fixes: a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6") Reported-by: syzbot+62cbf263225ae13ff153@syzkaller.appspotmail.com Link: https://lore.kernel.org/r/0000000000001c12b30605378ce8@google.com/ Suggested-by: Willem de Bruijn willemdebruijn.kernel@gmail.com Signed-off-by: David Howells dhowells@redhat.com cc: Eric Dumazet edumazet@google.com cc: Willem de Bruijn willemdebruijn.kernel@gmail.com cc: "David S. Miller" davem@davemloft.net cc: David Ahern dsahern@kernel.org cc: Paolo Abeni pabeni@redhat.com cc: Jakub Kicinski kuba@kernel.org cc: netdev@vger.kernel.org cc: bpf@vger.kernel.org cc: syzkaller-bugs@googlegroups.com Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/l2tp/l2tp_ip6.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c index 307cf20b66491..f91542e2f6793 100644 --- a/net/l2tp/l2tp_ip6.c +++ b/net/l2tp/l2tp_ip6.c @@ -521,7 +521,6 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) */ if (len > INT_MAX - transhdrlen) return -EMSGSIZE; - ulen = len + transhdrlen;
/* Mirror BSD error message compatibility */ if (msg->msg_flags & MSG_OOB) @@ -645,6 +644,7 @@ 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; err = ip6_append_data(sk, ip_generic_getfrag, msg, ulen, transhdrlen, &ipc6, &fl6, (struct rt6_info *)dst,