Race Condition Affecting kernel-rt-debug package, versions *
Threat Intelligence
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Test your applications- Snyk IDSNYK-CENTOS7-KERNELRTDEBUG-7911887
- published5 Sept 2024
- disclosed4 Sept 2024
Introduced: 4 Sep 2024
CVE-2024-44991 (opens in a new tab)How to fix?
There is no fixed version for Centos:7 kernel-rt-debug.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-rt-debug package and not the kernel-rt-debug package as distributed by Centos.
See How to fix? for Centos:7 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
tcp: prevent concurrent execution of tcp_sk_exit_batch
Its possible that two threads call tcp_sk_exit_batch() concurrently, once from the cleanup_net workqueue, once from a task that failed to clone a new netns. In the latter case, error unwinding calls the exit handlers in reverse order for the 'failed' netns.
tcp_sk_exit_batch() calls tcp_twsk_purge(). Problem is that since commit b099ce2602d8 ("net: Batch inet_twsk_purge"), this function picks up twsk in any dying netns, not just the one passed in via exit_batch list.
This means that the error unwind of setup_net() can "steal" and destroy timewait sockets belonging to the exiting netns.
This allows the netns exit worker to proceed to call
WARN_ON_ONCE(!refcount_dec_and_test(&net->ipv4.tcp_death_row.tw_refcount));
without the expected 1 -> 0 transition, which then splats.
At same time, error unwind path that is also running inet_twsk_purge() will splat as well:
WARNING: .. at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 ... refcount_dec include/linux/refcount.h:351 [inline] inet_twsk_kill+0x758/0x9c0 net/ipv4/inet_timewait_sock.c:70 inet_twsk_deschedule_put net/ipv4/inet_timewait_sock.c:221 inet_twsk_purge+0x725/0x890 net/ipv4/inet_timewait_sock.c:304 tcp_sk_exit_batch+0x1c/0x170 net/ipv4/tcp_ipv4.c:3522 ops_exit_list+0x128/0x180 net/core/net_namespace.c:178 setup_net+0x714/0xb40 net/core/net_namespace.c:375 copy_net_ns+0x2f0/0x670 net/core/net_namespace.c:508 create_new_namespaces+0x3ea/0xb10 kernel/nsproxy.c:110
... because refcount_dec() of tw_refcount unexpectedly dropped to 0.
This doesn't seem like an actual bug (no tw sockets got lost and I don't see a use-after-free) but as erroneous trigger of debug check.
Add a mutex to force strict ordering: the task that calls tcp_twsk_purge() blocks other task from doing final _dec_and_test before mutex-owner has removed all tw sockets of dying netns.
References
- https://access.redhat.com/security/cve/CVE-2024-44991
- https://git.kernel.org/stable/c/565d121b69980637f040eb4d84289869cdaabedf
- https://git.kernel.org/stable/c/99580ae890ec8bd98b21a2a9c6668f8f1555b62e
- https://git.kernel.org/stable/c/e3d9de3742f4d5c47ae35f888d3023a5b54fcd2f
- https://git.kernel.org/stable/c/f6fd2dbf584a4047ba88d1369ff91c9851261ec1