net: bridge: mcast: fix use-after-free of a master VLAN's multicast context

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-80842
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-04 16:18:12 UTC
Updated2026-09-04 16:18:12 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: bridge: mcast: fix use-after-free of a master VLAN's multicast context br_multicast_toggle_one_vlan() clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before stopping a VLAN's multicast context. That is the teardown handshake: lockless readers gate on the flag through br_multicast_ctx_should_use() -> br_multicast_ctx_vlan_disabled(), so once it is cleared under the lock no reader can arm the context again. For a master VLAN the handshake never runs. __vlan_del() clears BRIDGE_VLAN_INFO_BRENTRY before calling br_vlan_put_master(), so br_multicast_toggle_one_vlan(masterv, false) returns early on !br_vlan_is_brentry(vlan): the flag stays set and br->multicast_lock is never taken. br_vlan_put_master() then drains the context in br_multicast_ctx_deinit() and frees the VLAN through call_rcu(), while a reader still inside rcu_read_lock() sees the context as enabled and re-arms it. The port and port-VLAN branch of the function has no br_vlan_is_brentry() test and flips the flag under br->multicast_lock, so it is not affected. The reader is the bridge transmit path. For a master VLAN br_multicast_rcv() selects brmctx = &vlan->br_mcast_ctx with pmctx = NULL, so IGMP sent to the bridge device re-arms the context's timers after br_multicast_ctx_deinit() has already stopped them. BUG: KASAN: slab-use-after-free in detach_if_pending+0x412/0x4a0 Write of size 8 at addr ffff88810ac39918 by task brmc/601 __mod_timer+0x51a/0xc50 br_multicast_host_join+0x25b/0x390 __br_multicast_add_group+0x468/0x530 br_ip4_multicast_add_group+0x1a0/0x260 br_multicast_rcv+0x2cda/0x61e0 br_dev_xmit+0x6c4/0x1540 Allocated by task 610: br_vlan_add+0x111/0xb40 br_vlan_info+0x370/0x3e0 Freed by task 0: kfree+0x1a7/0x4f0 rcu_core+0x7dc/0x10a0 Only test br_vlan_is_brentry() when enabling, like the br_multicast_ctx_vlan_global_disabled() test next to it. Disabling then always clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before br_multicast_ctx_deinit() drains the context.

Risk And Classification

EPSS: 0.001770000 probability, percentile 0.073030000 (date 2026-09-07)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 3afaaee2f972aec9059110953adb62fa3cf5c4bd git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 22226a2c3b90f15b0925f1464470d3baa6c5677e git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686 git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50 git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e c069f29da72324697aa4b7cab5b3647a7d24a575 git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 3f4752996735e0628af559aa8da1d872c2fac13b git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 57f94d3f4dee8b54d63cefddf1112be4656ef9e6 git Not specified
CNA Linux Linux affected 7b54aaaf53cb784411426c64482af0435f7c845e 50e5c6605cc9c2dd57bd2d1b3459674d19738983 git Not specified
CNA Linux Linux affected 5.15 Not specified
CNA Linux Linux unaffected 5.15 semver Not specified
CNA Linux Linux unaffected 5.15.220 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.187 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.156 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.108 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.49 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.13 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2.3 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/57f94d3f4dee8b54d63cefddf1112be4656ef9e6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3afaaee2f972aec9059110953adb62fa3cf5c4bd 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/22226a2c3b90f15b0925f1464470d3baa6c5677e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3f4752996735e0628af559aa8da1d872c2fac13b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c069f29da72324697aa4b7cab5b3647a7d24a575 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/50e5c6605cc9c2dd57bd2d1b3459674d19738983 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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