CVE-2026-74571 in Linux
Resumen
por MITRE • 2026-08-15
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. ]
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