CVE-2021-47281 ALSA: seq: Fix race of snd_seq_timer_open()

2024-05-2114:20:07

Linux

github.com

linux kernel

vulnerability

alsa

seq

fix

race

snd_seq_timer_open

timer instance

uaf

leftover timer

syzkaller

protection

concurrent

check

assignment

ebusy

registered

cve

AI Score

6.8

Confidence

Low

EPSS

Percentile

15.5%

SSVC

Exploitation

none

Automatable

Technical Impact

partial

JSON

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

ALSA: seq: Fix race of snd_seq_timer_open()

The timer instance per queue is exclusive, and snd_seq_timer_open()
should have managed the concurrent accesses. It looks as if it’s
checking the already existing timer instance at the beginning, but
it’s not right, because there is no protection, hence any later
concurrent call of snd_seq_timer_open() may override the timer
instance easily. This may result in UAF, as the leftover timer
instance can keep running while the queue itself gets closed, as
spotted by syzkaller recently.

For avoiding the race, add a proper check at the assignment of
tmr->timeri again, and return -EBUSY if it’s been already registered.

CNA Affected

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "bd7d88b0874f",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "536a7646c00a",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "83e197a8414c",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "sound/core/seq/seq_timer.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "unaffected",
        "version": "5.10.44",
        "versionType": "custom",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.12.11",
        "versionType": "custom",
        "lessThanOrEqual": "5.12.*"
      },
      {
        "status": "unaffected",
        "version": "5.13",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "sound/core/seq/seq_timer.c"
    ],
    "defaultStatus": "affected"
  }
]