ipv4: fix use-after-free in fib_nhc_update_mtu()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74656
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-22 16:16:39 UTC
Updated2026-08-22 16:16:39 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ipv4: fix use-after-free in fib_nhc_update_mtu() fib_nhc_update_mtu() walks the nexthop exception table under RTNL, but RTNL does not serialize this walk with PMTU exception updates. The walk uses rcu_dereference_protected() with a constant true condition without holding fnhe_lock. The following interleaving can therefore occur: CPU 0 CPU 1 fib_nhc_update_mtu() update_or_create_fnhe() load fnhe spin_lock_bh(&fnhe_lock) fnhe_remove_oldest() unlink fnhe kfree_rcu(fnhe, rcu) <quiescent state> access fnhe after grace period KASAN reported: BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410 Read of size 8 at addr ffff888107d49000 by task poc/90 Call Trace: fib_nhc_update_mtu+0x3df/0x410 fib_sync_mtu+0x7a/0xd0 fib_netdev_event+0x229/0x3f0 netif_set_mtu_ext+0x33a/0x570 dev_set_mtu+0x88/0x120 The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a pair and other writers serialize them with fnhe_lock. RCU alone prevents reclamation, but would still allow concurrent writers to leave a mixed pair. Walk the table under RCU and acquire fnhe_lock only while updating each exception. RCU keeps the current entry alive while the short critical section serializes its paired PMTU fields. This avoids holding the global lock while scanning all 2048 buckets for every nexthop.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 fd39e711866498ae94fcf9acf6f422a4f045b681 git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 e1e602d6b22d5cb1641c4459c487eb18bf569e0a git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 e00f7d2b5f2540a3415a229c982af7a25ff6362e git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 dfe388da13aa784851e5ebbea90afbb099075761 git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 5a28a4b22dde92f9d293b94236314b8d6181dc4a git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 63996ffc594d128ccec8fc0983f91effd2d3adc4 git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 ed503eaad62f20cdd5122d7c3078a648a99c8f16 git Not specified
CNA Linux Linux affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 bc5bde9ce3cc36502839dfe98e068f7303a50982 git Not specified
CNA Linux Linux affected b427832009b97a3ee412ef643a80b15372a7754d git Not specified
CNA Linux Linux affected 2b7e4c735933be79882aba2bed9afa789e03c62f git Not specified
CNA Linux Linux affected 8d59c3a6376bbc6dd3f7303968a719ffba75a4f1 git Not specified
CNA Linux Linux affected 9b4869cf385aa16f89c0f019eed4ec4e36aa441c git Not specified
CNA Linux Linux affected ff34695ced21e2dfa04d0fa1c5f6c35011fa8117 git Not specified
CNA Linux Linux affected 3.16.62 3.17 semver Not specified
CNA Linux Linux affected 4.4.162 4.5 semver Not specified
CNA Linux Linux affected 4.9.134 4.10 semver Not specified
CNA Linux Linux affected 4.14.77 4.15 semver Not specified
CNA Linux Linux affected 4.18.15 4.19 semver Not specified
CNA Linux Linux affected 4.19 Not specified
CNA Linux Linux unaffected 4.19 semver Not specified
CNA Linux Linux unaffected 5.10.265 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.216 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.183 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.152 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.104 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.45 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.9 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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