| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-49940: l2tp: prevent possible tunnel refcount underflow |
| |
| Description |
| =========== |
| |
| 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 Linux kernel CVE team has assigned CVE-2024-49940 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Fixed in 6.11.3 with commit f7415e60c25a6108cd7955a20b2e66b6251ffe02 |
| Fixed in 6.12 with commit 24256415d18695b46da06c93135f5b51c548b950 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2024-49940 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| net/l2tp/l2tp_core.c |
| net/l2tp/l2tp_core.h |
| net/l2tp/l2tp_netlink.c |
| net/l2tp/l2tp_ppp.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/f7415e60c25a6108cd7955a20b2e66b6251ffe02 |
| https://git.kernel.org/stable/c/24256415d18695b46da06c93135f5b51c548b950 |
