CVE-2021-47189 btrfs: fix memory ordering between normal and ordered work functions

2024-04-1018:56:28

Linux

www.cve.org

linux kernel

btrfs

vulnerability

memory ordering

ordering

async_chunk

inode

crash

arm64

bitops

barrier calls

access

work functions

execution

synchronized

thread

calling.

7.5 High

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

13.1%

JSON

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

&lt;registers omitted for brevity&gt;

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.

CNA Affected

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    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "fs/btrfs/async-thread.c"
    ],
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    ]
  }
]