CVE-2024-49940

Summary

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

l2tp: prevent possible tunnel refcount underflow

When a session is created, it sets a backpointer to its tunnel. When the session refcount drops to 0, l2tp_session_free drops the tunnel refcount if session->tunnel is non-NULL. However, session->tunnel is set in l2tp_session_create, before the tunnel refcount is incremented by l2tp_session_register, which leaves a small window where session->tunnel is non-NULL when the tunnel refcount hasn't been bumped.

Moving the assignment to l2tp_session_register is trivial but l2tp_session_create calls l2tp_session_set_header_len which uses session->tunnel to get the tunnel's encap. Add an encap arg to l2tp_session_set_header_len to avoid using session->tunnel.

If l2tpv3 sessions have colliding IDs, it is possible for l2tp_v3_session_get to race with l2tp_session_register and fetch a session which doesn't yet have session->tunnel set. Add a check for this case.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux3953ae7b218df4d1e544b98a393666f9ae58a78c < f7415e60c25a6108cd7955a20b2e66b6251ffe02affected
LinuxLinux3953ae7b218df4d1e544b98a393666f9ae58a78c < 24256415d18695b46da06c93135f5b51c548b950affected
LinuxLinuxb102bfc2a90d14f342580285782a9a51c74f7369affected
LinuxLinux10c15ddabbcf888922adbdd44ca3fecf6eab19d9affected
LinuxLinux8d1c650d452c53fcb3f02a7b1d772741639f89a4affected
LinuxLinux12b5fb58ac993c24210cf8cbc72d407d3a4e6490affected
LinuxLinuxaef37401b467a0b1a9517c69924a1d66937e0789affected
LinuxLinux3.2.99 < 3.3affected
LinuxLinux3.16.54 < 3.17affected
LinuxLinux4.4.225 < 4.5affected
LinuxLinux4.9.225 < 4.10affected
LinuxLinux4.14.182 < 4.15affected
LinuxLinux4.15affected
LinuxLinux0 < 4.15unaffected
LinuxLinux6.11.3 <= 6.11.*unaffected
LinuxLinux6.12 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References