CVE-2026-98102 — ipv6: mcast: fix RCU list diversion in ip6_mc_del1_src()

Affected: Linux

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

ipv6: mcast: fix RCU list diversion in ip6_mc_del1_src()

When removing a source filter whose count reaches zero, ip6_mc_del1_src() unlinks psf from pmc->mca_sources. If the filter was previously active, the code moved psf directly into pmc->mca_tomb by updating psf->sf_next.

Because pmc->mca_sources is traversed locklessly under RCU (e.g. by ipv6_chk_mcast_addr()), mutating psf->sf_next before a grace period elapses diverts concurrent readers to the tombstone list. Consequently, readers miss remaining active sources in pmc->mca_sources and improperly examine deleted tombstone entries.

Fix this by allocating a new tombstone node for pmc->mca_tomb (as done in sf_setstate()) and retiring the original psf via kfree_rcu().

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CVE-2026-98102 — ipv6: mcast: fix RCU list diversion in ip6_mc_del1_src()