CVE-2024-49940

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.

The following products are affected by CVE-2024-49940 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2024-49940.

URL	Resource
https://git.kernel.org/stable/c/24256415d18695b46da06c93135f5b51c548b950
https://git.kernel.org/stable/c/f7415e60c25a6108cd7955a20b2e66b6251ffe02
https://lore.kernel.org/linux-cve-announce/2024102127-CVE-2024-49940-1c88@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2024-49940
https://www.cve.org/CVERecord?id=CVE-2024-49940