CVE-2024-44991: tcp: prevent concurrent execution of tcp_sk_exit_batch
First published: Wed Sep 04 2024(Updated: )
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.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Linux kernel | >=6.1<6.1.107 | |
| Linux Linux kernel | >=6.2<6.6.48 | |
| Linux Linux kernel | >=6.7<6.10.7 | |
| Linux Linux kernel | =6.11-rc1 | |
| Linux Linux kernel | =6.11-rc2 | |
| Linux Linux kernel | =6.11-rc3 | |
| Linux Linux kernel | =6.11-rc4 | |
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.119-1 6.11.10-1 6.12.5-1 |
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Reference Links
- 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
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-44991
- https://nvd.nist.gov/vuln/detail/CVE-2024-44991
- https://launchpad.net/bugs/cve/CVE-2024-44991
- https://security-tracker.debian.org/tracker/CVE-2024-44991
- https://ubuntu.com/security/CVE-2024-44991
- https://git.kernel.org/linus/565d121b69980637f040eb4d84289869cdaabedf
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