Use After Free Affecting kernel-rt-kvm package, versions *


Severity

medium

    Threat Intelligence

    EPSS
    0.04% (6th percentile)

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  • Snyk ID SNYK-CENTOS7-KERNELRTKVM-6302974
  • published 28 Feb 2024
  • disclosed 27 Feb 2024

How to fix?

There is no fixed version for Centos:7 kernel-rt-kvm.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-rt-kvm package and not the kernel-rt-kvm 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:

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

CVSS Scores

version 3.1
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Snyk

7.3 medium
  • Attack Vector (AV)
    Local
  • Attack Complexity (AC)
    Low
  • Privileges Required (PR)
    Low
  • User Interaction (UI)
    None
  • Scope (S)
    Unchanged
  • Confidentiality (C)
    High
  • Integrity (I)
    Low
  • Availability (A)
    High
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NVD

7.8 high
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SUSE

5.5 medium
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Red Hat

7.3 high