CVE-2024-49940 (GCVE-0-2024-49940)
Vulnerability from cvelistv5
Published
2024-10-21 18:01
Modified
2026-05-23 15:54
Severity ?
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 3953ae7b218df4d1e544b98a393666f9ae58a78c
Version: 3953ae7b218df4d1e544b98a393666f9ae58a78c
Version: b102bfc2a90d14f342580285782a9a51c74f7369
Version: 10c15ddabbcf888922adbdd44ca3fecf6eab19d9
Version: 8d1c650d452c53fcb3f02a7b1d772741639f89a4
Version: 12b5fb58ac993c24210cf8cbc72d407d3a4e6490
Version: aef37401b467a0b1a9517c69924a1d66937e0789
Version: 3.2.99   ≤
Version: 3.16.54   ≤
Version: 4.4.225   ≤
Version: 4.9.225   ≤
Version: 4.14.182   ≤
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: prevent possible tunnel refcount underflow\n\nWhen a session is created, it sets a backpointer to its tunnel. When\nthe session refcount drops to 0, l2tp_session_free drops the tunnel\nrefcount if session-\u003etunnel is non-NULL. However, session-\u003etunnel is\nset in l2tp_session_create, before the tunnel refcount is incremented\nby l2tp_session_register, which leaves a small window where\nsession-\u003etunnel is non-NULL when the tunnel refcount hasn\u0027t been\nbumped.\n\nMoving the assignment to l2tp_session_register is trivial but\nl2tp_session_create calls l2tp_session_set_header_len which uses\nsession-\u003etunnel to get the tunnel\u0027s encap. Add an encap arg to\nl2tp_session_set_header_len to avoid using session-\u003etunnel.\n\nIf l2tpv3 sessions have colliding IDs, it is possible for\nl2tp_v3_session_get to race with l2tp_session_register and fetch a\nsession which doesn\u0027t yet have session-\u003etunnel set. Add a check for\nthis case."
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