CVE-2021-47488

2024-05-2209:15:10

416baaa9-dc9f-4396-8d5f-8c081fb06d67

web.nvd.nist.gov

linux kernel

cgroup

vulnerability

fix

memory leak

config_cgroup_bpf

mount

umount

percpu_ref

percpu_ref_init

cgroup_setup_root

cgroup_bpf_offline

cgroup_kill_sb

bpf

cgroup_bpf_release

6.8 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

15.5%

JSON

In the Linux kernel, the following vulnerability has been resolved:

cgroup: Fix memory leak caused by missing cgroup_bpf_offline

When enabling CONFIG_CGROUP_BPF, kmemleak can be observed by running
the command as below:

$mount -t cgroup -o none,name=foo cgroup cgroup/
$umount cgroup/

unreferenced object 0xc3585c40 (size 64):
comm “mount”, pid 425, jiffies 4294959825 (age 31.990s)
hex dump (first 32 bytes):
01 00 00 80 84 8c 28 c0 00 00 00 00 00 00 00 00 …(…
00 00 00 00 00 00 00 00 6c 43 a0 c3 00 00 00 00 …lC…
backtrace:
[<e95a2f9e>] cgroup_bpf_inherit+0x44/0x24c
[<1f03679c>] cgroup_setup_root+0x174/0x37c
[<ed4b0ac5>] cgroup1_get_tree+0x2c0/0x4a0
[<f85b12fd>] vfs_get_tree+0x24/0x108
[<f55aec5c>] path_mount+0x384/0x988
[<e2d5e9cd>] do_mount+0x64/0x9c
[<208c9cfe>] sys_mount+0xfc/0x1f4
[<06dd06e0>] ret_fast_syscall+0x0/0x48
[<a8308cb3>] 0xbeb4daa8

This is because that since the commit 2b0d3d3e4fcf (“percpu_ref: reduce
memory footprint of percpu_ref in fast path”) root_cgrp->bpf.refcnt.data
is allocated by the function percpu_ref_init in cgroup_bpf_inherit which
is called by cgroup_setup_root when mounting, but not freed along with
root_cgrp when umounting. Adding cgroup_bpf_offline which calls
percpu_ref_kill to cgroup_kill_sb can free root_cgrp->bpf.refcnt.data in
umount path.

This patch also fixes the commit 4bfc0bb2c60e (“bpf: decouple the lifetime
of cgroup_bpf from cgroup itself”). A cgroup_bpf_offline is needed to do a
cleanup that frees the resources which are allocated by cgroup_bpf_inherit
in cgroup_setup_root.

And inside cgroup_bpf_offline, cgroup_get() is at the beginning and
cgroup_put is at the end of cgroup_bpf_release which is called by
cgroup_bpf_offline. So cgroup_bpf_offline can keep the balance of
cgroup’s refcount.

Affected configurations

Vulners

Node

linuxlinux_kernelRange5.3–5.10.77

linuxlinux_kernelRange5.11.0–5.14.16

linuxlinux_kernelRange5.15.0≥

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/cgroup/cgroup.c"
    ],
    "versions": [
      {
        "version": "4bfc0bb2c60e",
        "lessThan": "01599bf7cc2b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "4bfc0bb2c60e",
        "lessThan": "b529f88d9388",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "4bfc0bb2c60e",
        "lessThan": "04f8ef5643bc",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/cgroup/cgroup.c"
    ],
    "versions": [
      {
        "version": "5.3",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.3",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.77",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.14.16",
        "lessThanOrEqual": "5.14.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]