net: fix use-after-free in tw_timer_handler

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2021-46936
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2024-02-27 10:15:08 UTC
Updated2026-08-04 10:16:37 UTC
DescriptionIn 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

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Problem Types: CWE-416

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 15579e1301f856ad9385d720c9267c11032a5022 git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 e73164e89d1be561228a4534e1091369ee4ba41a git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 5c2fe20ad37ff56070ae0acb34152333976929b4 git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 a8e1944b44f94f5c5f530e434c5eaee787254566 git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 fe5838c22b986c1190f1dce9aa09bf6a491c1a69 git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 2386e81a1d277f540e1285565c9d41d531bb69d4 git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 08eacbd141e2495d2fcdde84358a06c4f95cbb13 git Not specified
CNA Linux Linux affected 61a7e26028b94805fd686a6dc9dbd9941f8f19b0 e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 git Not specified
CNA Linux Linux affected 2.6.27 Not specified
CNA Linux Linux unaffected 2.6.27 semver Not specified
CNA Linux Linux unaffected 4.4.298 4.4.* semver Not specified
CNA Linux Linux unaffected 4.9.296 4.9.* semver Not specified
CNA Linux Linux unaffected 4.14.261 4.14.* semver Not specified
CNA Linux Linux unaffected 4.19.224 4.19.* semver Not specified
CNA Linux Linux unaffected 5.4.170 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.90 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.13 5.15.* semver Not specified
CNA Linux Linux unaffected 5.16 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
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