CVE-2021-46936 net: fix use-after-free in tw_timer_handler

2024-02-2709:44:02

Linux

www.cve.org

linux kernel

vulnerability

use-after-free

tw_timer_handler

net

ipv4_mib

net statistics

AI Score

7.7

Confidence

High

EPSS

Percentile

5.1%

JSON

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:
 &lt;IRQ&gt;
 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

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/ipv4/af_inet.c"
    ],
    "versions": [
      {
        "version": "61a7e26028b9",
        "lessThan": "15579e1301f8",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "e73164e89d1b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "5c2fe20ad37f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "a8e1944b44f9",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "fe5838c22b98",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "2386e81a1d27",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "08eacbd141e2",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "61a7e26028b9",
        "lessThan": "e22e45fc9e41",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/ipv4/af_inet.c"
    ],
    "versions": [
      {
        "version": "2.6.27",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "2.6.27",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.4.298",
        "lessThanOrEqual": "4.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.9.296",
        "lessThanOrEqual": "4.9.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.14.261",
        "lessThanOrEqual": "4.14.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.19.224",
        "lessThanOrEqual": "4.19.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.4.170",
        "lessThanOrEqual": "5.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.90",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.13",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.16",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]