ipv6: mcast: use copy-on-write RCU updates in ip6_mc_source()

Summary

In the Linux kernel, the following vulnerability has been resolved: ipv6: mcast: use copy-on-write RCU updates in ip6_mc_source() pmc->sflist is read locklessly under rcu_read_lock() by inet6_mc_check() during packet reception in the UDP and RAW multicast receive paths. ip6_mc_source() mutated psl->sl_addr and psl->sl_count in-place when adding or removing a source filter. Additionally, when expanding the filter buffer, newpsl was published via rcu_assign_pointer() before writing the new source into the array. Because 16-byte struct in6_addr writes are not atomic and array shifting is not synchronized with RCU readers, concurrent readers in inet6_mc_check() could read torn IPv6 addresses or observe duplicated/missed source entries. Fix this by switching ip6_mc_source() to copy-on-write RCU updates: allocate and fully populate newpsl before publishing it via rcu_assign_pointer(), and reclaim the old filter via kfree_rcu(), matching ip6_mc_msfilter(). Also remove the now unused IP6_SFBLOCK macro.

Timeline

1. Sep 25, 2026, 10:35 AM UTCCVE published
2. Oct 19, 2026, 9:13 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 882ba1f73c06831f2a21044ebd8864c485ac04f2 · fixed in ac51321d3b2391860a935820ebcf4d8b9bb16a8a; From 882ba1f73c06831f2a21044ebd8864c485ac04f2 · fixed in dba00514bf668c26cb4900e9f0da84bf96bf065a; From 882ba1f73c06831f2a21044ebd8864c485ac04f2 · fixed in 2c2091e2ee93049fc513ad1e6c99d8b6c809f467; From 882ba1f73c06831f2a21044ebd8864c485ac04f2 · fixed in 20db91a052332ef5552bd2f651ffb9db911cf67b; From 882ba1f73c06831f2a21044ebd8864c485ac04f2 · fixed in c073d1b070f171d206b19c98d71739a97f15b3f1; From 5.10.261 · fixed in 5.11

• Linux Linux

  5.13

• KernelLinux

  From 5.13.0 · fixed in 6.6.158; From 6.7.0 · fixed in 6.12.112; From 6.13.0 · fixed in 6.18.53; From 6.19.0 · fixed in 7.2.7

References 5