CVE-2021-47189

Summary

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

btrfs: fix memory ordering between normal and ordered work functions

Ordered work functions aren't guaranteed to be handled by the same thread which executed the normal work functions. The only way execution between normal/ordered functions is synchronized is via the WORK_DONE_BIT, unfortunately the used bitops don't guarantee any ordering whatsoever.

This manifested as seemingly inexplicable crashes on ARM64, where async_chunk::inode is seen as non-null in async_cow_submit which causes submit_compressed_extents to be called and crash occurs because async_chunk::inode suddenly became NULL. The call trace was similar to:

pc : submit_compressed_extents+0x38/0x3d0
lr : async_cow_submit+0x50/0xd0
sp : ffff800015d4bc20

<registers omitted for brevity>

Call trace:
 submit_compressed_extents+0x38/0x3d0
 async_cow_submit+0x50/0xd0
 run_ordered_work+0xc8/0x280
 btrfs_work_helper+0x98/0x250
 process_one_work+0x1f0/0x4ac
 worker_thread+0x188/0x504
 kthread+0x110/0x114
 ret_from_fork+0x10/0x18

Fix this by adding respective barrier calls which ensure that all accesses preceding setting of WORK_DONE_BIT are strictly ordered before setting the flag. At the same time add a read barrier after reading of WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads would be strictly ordered after reading the bit. This in turn ensures are all accesses before WORK_DONE_BIT are going to be strictly ordered before any access that can occur in ordered_func.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < bd660a20fea3ec60a49709ef5360f145ec0fe779affected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < 637d652d351fd4f263ef302dc52f3971d314e500affected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < 804a9d239ae9cbe88e861a7cd62319cc6ec7b136affected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < ed058d735a70f4b063323f1a7bb33cda0f987513affected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < 670f6b3867c8f0f11e5097f353b164cecfec6179affected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < 6adbc07ebcaf8bead08b21687d49e0fc94400987affected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < 47e6f9f69153247109042010f3a77579e9dc61ffaffected
LinuxLinux08a9ff3264181986d1d692a4e6fce3669700c9f8 < 45da9c1767ac31857df572f0a909fbe88fd5a7e9affected
LinuxLinux3.15affected
LinuxLinux0 < 3.15unaffected
LinuxLinux4.4.293 <= 4.4.*unaffected
LinuxLinux4.9.291 <= 4.9.*unaffected
LinuxLinux4.14.256 <= 4.14.*unaffected
LinuxLinux4.19.218 <= 4.19.*unaffected
LinuxLinux5.4.162 <= 5.4.*unaffected
LinuxLinux5.10.82 <= 5.10.*unaffected
LinuxLinux5.15.5 <= 5.15.*unaffected
LinuxLinux5.16 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

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

CVE Program Container

Additional References

References