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l2tp: pass correct message length to ip6_append_data

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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: 9d4c75800f ("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>
Link: https://lore.kernel.org/r/20240220122156.43131-1-tparkin@katalix.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Tom Parkin 2024-02-20 12:21:56 +00:00 committed by Paolo Abeni
parent 9ff2794306
commit 359e54a93a
1 changed files with 1 additions and 1 deletions
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2
net/l2tp/l2tp_ip6.c
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@ -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,