CVE-2022-49999

published 2025-06-18

CVE-2022-49999: In the Linux kernel, the following vulnerability has been resolved: btrfs: fix space cache corruption and potential double allocations When testing space_cache…

Priority P3 38 high 7.8 CVSS 3.1

AV L AC L PR L UI N S U C H I H A H

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

btrfs: fix space cache corruption and potential double allocations

When testing space_cache v2 on a large set of machines, we encountered a
few symptoms:

1. "unable to add free space :-17" (EEXIST) errors.
2. Missing free space info items, sometimes caught with a "missing free
space info for X" error.
3. Double-accounted space: ranges that were allocated in the extent tree
and also marked as free in the free space tree, ranges that were
marked as allocated twice in the extent tree, or ranges that were
marked as free twice in the free space tree. If the latter made it
onto disk, the next reboot would hit the BUG_ON() in
add_new_free_space().
4. On some hosts with no on-disk corruption or error messages, the
in-memory space cache (dumped with drgn) disagreed with the free
space tree.

All of these symptoms have the same underlying cause: a race between
caching the free space for a block group and returning free space to the
in-memory space cache for pinned extents causes us to double-add a free
range to the space cache. This race exists when free space is cached
from the free space tree (space_cache=v2) or the extent tree
(nospace_cache, or space_cache=v1 if the cache needs to be regenerated).
struct btrfs_block_group::last_byte_to_unpin and struct
btrfs_block_group::progress are supposed to protect against this race,
but commit d0c2f4fa555e ("btrfs: make concurrent fsyncs wait less when
waiting for a transaction commit") subtly broke this by allowing
multiple transactions to be unpinning extents at the same time.

Specifically, the race is as follows:

1. An extent is deleted from an uncached block group in transaction A.
2. btrfs_commit_transaction() is called for transaction A.
3. btrfs_run_delayed_refs() -> __btrfs_free_extent() runs the delayed
ref for the deleted extent.
4. __btrfs_free_extent() -> do_free_extent_accounting() ->
add_to_free_space_tree() adds the deleted extent back to the fre

Affected

11 ranges

Vendor	Product	Version range	Fixed in
debian	linux	< linux 6.0.2-1 (bookworm)	linux 6.0.2-1 (bookworm)
linux	linux	—	—
linux	linux	>= d0c2f4fa555e70324ec2a129b822ab58f172cc62 < 92dc4c1a8e58bcc7a183a4c86b055c24cc88d967	92dc4c1a8e58bcc7a183a4c86b055c24cc88d967
linux	linux	>= d0c2f4fa555e70324ec2a129b822ab58f172cc62 < a2e54eb64229f07f917b05d0c323604fda9b89f7	a2e54eb64229f07f917b05d0c323604fda9b89f7
linux	linux	>= d0c2f4fa555e70324ec2a129b822ab58f172cc62 < ced8ecf026fd8084cf175530ff85c76d6085d715	ced8ecf026fd8084cf175530ff85c76d6085d715
linux	linux_kernel	—	—
linux	linux_kernel	>= 0 < 6.0.2-1	6.0.2-1
linux	linux_kernel	>= 0 < 6.0.2-1	6.0.2-1
linux	linux_kernel	>= 0 < 6.0.2-1	6.0.2-1
linux	linux_kernel	>= 5.12 < 5.15.65	5.15.65
linux	linux_kernel	>= 5.16 < 5.19.6	5.19.6

CVSS provenance

nvd v3.1 7.8 HIGH CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

osv 7.8 HIGH

vendor_debian 7.8 HIGH

vendor_redhat 7.8 HIGH

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