CVE-2026-74571: BTRFS NULL ptr deref on rescue=ibadroots mount
CVE-2026-74571 Published on August 15, 2026
btrfs: skip global block reserve accounting for rescue mounts
In the Linux kernel, the following vulnerability has been resolved:
btrfs: skip global block reserve accounting for rescue mounts
[BUG]
Mounting with rescue=ibadroots after corrupting the block group tree
root triggers a NULL pointer dereference:
BUG: kernel NULL pointer dereference, address: 0000000000000100
RIP: 0010:btrfs_update_global_block_rsv+0x9d/0x1c0 [btrfs]
Call Trace:
fill_dummy_bgs+0xd4/0x120 [btrfs]
open_ctree+0xc6e/0x1ca0 [btrfs]
btrfs_get_tree+0x50d/0xa40 [btrfs]
The same crash occurs with a corrupted raid stripe tree root, via
btrfs_read_block_groups() instead of fill_dummy_bgs().
[CAUSE]
With rescue=ibadroots, btrfs_read_roots() allows the mount to continue
when either root cannot be read, leaving the corresponding root pointer
NULL while its on-disk feature bit remains set.
btrfs_update_global_block_rsv() then dereferences the missing root based
on the feature bit alone.
[FIX]
Rescue mounts are fully read-only and cannot start transactions, so the
global reserve is never consumed. Under btrfs_is_full_ro(), mark the
reserve as full and return before performing the accounting.
And since we need to check if the fs is mount fully RO, export
fs_is_full_ro() as btrfs_is_full_ro(), and move it to fs.h.
[ Squash the fs_is_full_ro() export commit into this one. ]
Products Associated with CVE-2026-74571
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Affected Versions
Linux:- Version 8dbfc14fc736eb701089aff09645c3d4ad3decb1 and below 076349e4c8d11f6b58c4549976a513b2b4dc6df2 is affected.
- Version 8dbfc14fc736eb701089aff09645c3d4ad3decb1 and below 51a0e8399858621442807a26057bcd1cd3ced046 is affected.
- Version cbec34d3021d47007a0334c634f7053dbaf93d02 is affected.
- Version 1e8087589b5cf6fa17adaf57b64cf1656d77dfec is affected.
- Version 6.1.43 and below 6.2 is affected.
- Version 6.4.8 and below 6.5 is affected.
- Version 6.5 is affected.
- Before 6.5 is unaffected.
- Version 7.1.8, <= 7.1.* is unaffected.
- Version 7.2-rc6, <= * is unaffected.