CVE-2026-31680 - net: ipv6: flowlabel: defer exclusive option free until RCU teardown

CVE-2026-31680 - net: ipv6: flowlabel: defer exclusive option free until RCU teardown

https://cvefeed.io/rssfeed/latest.atom / Sat, 04/25/2026 - 14:20
CVE ID :CVE-2026-31680
Published : April 25, 2026, 9:16 a.m. | 2 hours, 57 minutes ago
Description :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.
Severity: 0.0 | NA
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