In the Linux kernel, the following vulnerability has been resolved:

tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)

When MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535).
This is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.

However, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel.
If a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will
be mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer
dereference because local TCP packets do not use frag_list.

Fix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from
ip6_default_advmss() when MTU is large.

Also update the stale comment in ip6_default_advmss() which suggested
that IPV6_MAXPLEN is returned to mean "any MSS".

https://git.kernel.org/stable/c/21f69ac1879bb970588d5e7c12a96e6542f7c1a7

https://git.kernel.org/stable/c/2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22

https://git.kernel.org/stable/c/560b33b434e922ef97f9ff23aa2e909ef7aacd5c

https://git.kernel.org/stable/c/572fff10819dfc359298d1f774839e76a4d96f93

https://git.kernel.org/stable/c/8e6214a530c03e341dc1b0a846c8f2b716b3551a

https://git.kernel.org/stable/c/a210791f33345aa87187f7d7a9f3b9b7f4a28e6d

https://git.kernel.org/stable/c/c0db3dc2ac323b6c4b76adede3b355a9daa6dea8

https://git.kernel.org/stable/c/d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e

[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","programFiles":["net/ipv6/route.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","versions":[{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"560b33b434e922ef97f9ff23aa2e909ef7aacd5c","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"21f69ac1879bb970588d5e7c12a96e6542f7c1a7","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"c0db3dc2ac323b6c4b76adede3b355a9daa6dea8","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"572fff10819dfc359298d1f774839e76a4d96f93","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"8e6214a530c03e341dc1b0a846c8f2b716b3551a","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"a210791f33345aa87187f7d7a9f3b9b7f4a28e6d","versionType":"git","status":"affected"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","lessThan":"2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22","versionType":"git","status":"affected"}]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","programFiles":["net/ipv6/route.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","versions":[{"version":"4.8","status":"affected"},{"version":"0","lessThan":"4.8","versionType":"semver","status":"unaffected"},{"version":"5.10.261","lessThanOrEqual":"5.10.*","versionType":"semver","status":"unaffected"},{"version":"5.15.212","lessThanOrEqual":"5.15.*","versionType":"semver","status":"unaffected"},{"version":"6.1.178","lessThanOrEqual":"6.1.*","versionType":"semver","status":"unaffected"},{"version":"6.6.145","lessThanOrEqual":"6.6.*","versionType":"semver","status":"unaffected"},{"version":"6.12.97","lessThanOrEqual":"6.12.*","versionType":"semver","status":"unaffected"},{"version":"6.18.40","lessThanOrEqual":"6.18.*","versionType":"semver","status":"unaffected"},{"version":"7.1.5","lessThanOrEqual":"7.1.*","versionType":"semver","status":"unaffected"},{"version":"7.2-rc1","lessThanOrEqual":"*","versionType":"original_commit_for_fix","status":"unaffected"}]}]