Linux kernel: RCU race in ipv6 flowlabel /proc reading leads to crash
CVE-2026-31680 Published on April 25, 2026
net: ipv6: flowlabel: defer exclusive option free until RCU teardown
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.
Products Associated with CVE-2026-31680
Want to know whenever a new CVE is published for Linux Kernel? stack.watch will email you.
Affected Versions
Linux:- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 4b6798024f7b2d535f3db1002c760143cdbd1bd3 is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827 is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 5a6b15f861b7c1304949e3350d23490a5fe429fd is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8 is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 8027964931785cb73d520ac70a342a3dc16c249b is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 414726b69921fe6355ae453f5b35e68dd078342a is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 572ce62778519a7d4d1c15f55dd2e45a474133c4 is affected.
- Version d3aedd5ebd4b0b925b0bcda548066803e1318499 and below 9ca562bb8e66978b53028fa32b1a190708e6a091 is affected.
- Version 3.9 is affected.
- Before 3.9 is unaffected.
- Version 5.10.253, <= 5.10.* is unaffected.
- Version 5.15.203, <= 5.15.* is unaffected.
- Version 6.1.168, <= 6.1.* is unaffected.
- Version 6.6.134, <= 6.6.* is unaffected.
- Version 6.12.81, <= 6.12.* is unaffected.
- Version 6.18.22, <= 6.18.* is unaffected.
- Version 6.19.12, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.