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Ubuntu: USN-6739-1 (CVE-2021-46936): Linux kernel vulnerabilities

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Ubuntu: USN-6739-1 (CVE-2021-46936): Linux kernel vulnerabilities

Severity
7
CVSS
(AV:L/AC:L/Au:S/C:C/I:C/A:C)
Published
02/27/2024
Created
04/22/2024
Added
04/22/2024
Modified
01/30/2025

Description

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

Solution(s)

  • ubuntu-upgrade-linux-image-4-4-0-1130-aws
  • ubuntu-upgrade-linux-image-4-4-0-1131-kvm
  • ubuntu-upgrade-linux-image-4-4-0-1168-aws
  • ubuntu-upgrade-linux-image-4-4-0-253-generic
  • ubuntu-upgrade-linux-image-4-4-0-253-lowlatency
  • ubuntu-upgrade-linux-image-aws
  • ubuntu-upgrade-linux-image-generic
  • ubuntu-upgrade-linux-image-generic-lts-xenial
  • ubuntu-upgrade-linux-image-kvm
  • ubuntu-upgrade-linux-image-lowlatency
  • ubuntu-upgrade-linux-image-lowlatency-lts-xenial
  • ubuntu-upgrade-linux-image-virtual
  • ubuntu-upgrade-linux-image-virtual-lts-xenial

References

  • https://attackerkb.com/topics/cve-2021-46936
  • CVE - 2021-46936
  • USN-6739-1
  • 查看数 705
  • 已创建
  • 最后回复

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