ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-68398
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-10 13:20:33 UTC
Updated2026-08-10 13:20:33 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan) It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences. The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree(): close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch) For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU. The bug is reachable by an unprivileged user. Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 4bb84e964ff0fe0a171c965362de72f9820dbce9 git Not specified
CNA Linux Linux affected ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 3ab32218d7182705dae5c86f13925f458072da2c git Not specified
CNA Linux Linux affected ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa git Not specified
CNA Linux Linux affected ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 06213c85d8c0994f786c093b8b2a517987943ca6 git Not specified
CNA Linux Linux affected ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 ec4215683e47424c9c4762fd3c60f552a3119142 git Not specified
CNA Linux Linux affected d36e5ba7bbed5d7bd26e8609ffed503c2def401b git Not specified
CNA Linux Linux affected 9bcc0508576b2d50efd958f2ea1c5906749c2c89 git Not specified
CNA Linux Linux affected c2984681fe15cfb803a9132aaaf1140ab20a72c1 git Not specified
CNA Linux Linux affected 5803ecd7f6ac6f747582e775caa62ac9d0489261 git Not specified
CNA Linux Linux affected 26f8819ddd10141ebe7bbce700fbab36bfa5f478 git Not specified
CNA Linux Linux affected 3.2.99 3.3 semver Not specified
CNA Linux Linux affected 3.16.54 3.17 semver Not specified
CNA Linux Linux affected 4.4.225 4.5 semver Not specified
CNA Linux Linux affected 4.9.225 4.10 semver Not specified
CNA Linux Linux affected 4.14.182 4.15 semver Not specified
CNA Linux Linux affected 4.15 Not specified
CNA Linux Linux unaffected 4.15 semver Not specified
CNA Linux Linux unaffected 6.6.148 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.101 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.42 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.6 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc4 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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