Vulnerability CVE-2021-47189

Vulnerability CVE-2021-47189

Published: 2024-04-10

Description:

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.

References:

https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779

https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500

https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136

https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513

https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179

https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987

https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff

https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9

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