CVE-2026-31680

Summary

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

net: ipv6: flowlabel: defer exclusive option free until RCU teardown

ip6fl_seq_show() walks the global flowlabel hash under the seq-file RCU read-side lock and prints fl->opt->opt_nflen when an option block is present.

Exclusive flowlabels currently free fl->opt as soon as fl->users drops to zero in fl_release(). However, the surrounding struct ip6_flowlabel remains visible in the global hash table until later garbage collection removes it and fl_free_rcu() finally tears it down.

A concurrent /proc/net/ip6_flowlabel reader can therefore race that early kfree() and dereference freed option state, triggering a crash in ip6fl_seq_show().

Fix this by keeping fl->opt alive until fl_free_rcu(). That matches the lifetime already required for the enclosing flowlabel while readers can still reach it under RCU.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3
• https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827
• https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd
• https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8
• https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b
• https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a
• https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4
• https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091

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