CVE-2021-46936High· 7.8▾ TwilightIn 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: ffffde49a863d…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 42.9 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Aug 4.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.2%
0.2% → 0.2%
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
linux_kernel >= 2.6.27, < 4.4.298linux_kernel >= 4.5.0, < 4.9.296linux_kernel >= 4.10.0, < 4.14.261linux_kernel >= 4.15.0, < 4.19.224linux_kernel >= 4.20.0, < 5.4.170linux_kernel >= 5.5.0, < 5.10.90linux_kernel >= 5.11.0, < 5.15.13Upgrade past the affected range:
linux_kernel 5.15.13Connected by shared product, vendor, weakness, or advisory.
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