CVE-2021-46936: net: fix use-after-free in tw_timer_handler
First published: Tue Feb 27 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: net: fix use-after-free in tw_timer_handler A real world panic issue was found as follow in Linux 5.4. BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Call Trace: <IRQ> call_timer_fn+0x2b/0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP. The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers. This bug is not introduced by commit f2bf415cfed7 ("mib: add net to NET_ADD_STATS_BH") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 ("mib: put net statistics on struct net") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed. Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails. [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Linux kernel | >=2.6.27<4.4.298 | |
| Linux Linux kernel | >=4.5.0<4.9.296 | |
| Linux Linux kernel | >=4.10.0<4.14.261 | |
| Linux Linux kernel | >=4.15.0<4.19.224 | |
| Linux Linux kernel | >=4.20.0<5.4.170 | |
| Linux Linux kernel | >=5.5.0<5.10.90 | |
| Linux Linux kernel | >=5.11.0<5.15.13 | |
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.119-1 6.12.6-1 6.12.8-1 |
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Reference Links
- https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13
- https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022
- https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4
- https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4
- https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566
- https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0
- https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a
- https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69
- https://launchpad.net/bugs/cve/CVE-2021-46936
- https://git.kernel.org/linus/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0
- https://security-tracker.debian.org/tracker/CVE-2021-46936
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-46936
- https://nvd.nist.gov/vuln/detail/CVE-2021-46936
- https://ubuntu.com/security/CVE-2021-46936
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