CVE-2021-47281

Summary

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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < bd7d88b0874f82f7b29d1a53e574cedaf23166baaffected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 536a7646c00a0f14fee49e5e313109e5da2f6031affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 83e197a8414c0ba545e7e3916ce05f836f349273affected
LinuxLinux2.6.12affected
LinuxLinux0 < 2.6.12unaffected
LinuxLinux5.10.44 <= 5.10.*unaffected
LinuxLinux5.12.11 <= 5.12.*unaffected
LinuxLinux5.13 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

CVE Program Container

Additional References

References