CVE-2024-26752

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CVE-2024-26752

Summary: l2tp: pass correct message length to ip6_append_data

Details: In the Linux kernel, the following vulnerability has been resolved: l2tp: pass correct message length to ip6_append_data 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.

References: https://git.kernel.org/stable/c/0da15a70395182ee8cb75716baf00dddc0bea38d, https://git.kernel.org/stable/c/13cd1daeea848614e585b2c6ecc11ca9c8ab2500, https://git.kernel.org/stable/c/359e54a93ab43d32ee1bff3c2f9f10cb9f6b6e79, https://git.kernel.org/stable/c/4c3ce64bc9d36ca9164dd6c77ff144c121011aae, https://git.kernel.org/stable/c/804bd8650a3a2bf3432375f8c97d5049d845ce56, https://git.kernel.org/stable/c/83340c66b498e49353530e41542500fc8a4782d6, https://git.kernel.org/stable/c/c1d3a84a67db910ce28a871273c992c3d7f9efb5, https://git.kernel.org/stable/c/dcb4d14268595065c85dc5528056713928e17243, https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html, https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html, https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/26xxx/CVE-2024-26752.json, https://nvd.nist.gov/vuln/detail/CVE-2024-26752, https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git