CVE-2026-23214

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

btrfs: reject new transactions if the fs is fully read-only

[BUG]

There is a bug report where a heavily fuzzed fs is mounted with all

rescue mount options, which leads to the following warnings during

unmount:

BTRFS: Transaction aborted (error -22)

Modules linked in:

CPU: 0 UID: 0 PID: 9758 Comm: repro.out Not tainted

6.19.0-rc5-00002-gb71e635feefc #7 PREEMPT(full)

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014

RIP: 0010:find_free_extent_update_loop fs/btrfs/extent-tree.c:4208 [inline]

RIP: 0010:find_free_extent+0x52f0/0x5d20 fs/btrfs/extent-tree.c:4611

Call Trace:

<TASK>

btrfs_reserve_extent+0x2cd/0x790 fs/btrfs/extent-tree.c:4705

btrfs_alloc_tree_block+0x1e1/0x10e0 fs/btrfs/extent-tree.c:5157

btrfs_force_cow_block+0x578/0x2410 fs/btrfs/ctree.c:517

btrfs_cow_block+0x3c4/0xa80 fs/btrfs/ctree.c:708

btrfs_search_slot+0xcad/0x2b50 fs/btrfs/ctree.c:2130

btrfs_truncate_inode_items+0x45d/0x2350 fs/btrfs/inode-item.c:499

btrfs_evict_inode+0x923/0xe70 fs/btrfs/inode.c:5628

evict+0x5f4/0xae0 fs/inode.c:837

__dentry_kill+0x209/0x660 fs/dcache.c:670

finish_dput+0xc9/0x480 fs/dcache.c:879

shrink_dcache_for_umount+0xa0/0x170 fs/dcache.c:1661

generic_shutdown_super+0x67/0x2c0 fs/super.c:621

kill_anon_super+0x3b/0x70 fs/super.c:1289

btrfs_kill_super+0x41/0x50 fs/btrfs/super.c:2127

deactivate_locked_super+0xbc/0x130 fs/super.c:474

cleanup_mnt+0x425/0x4c0 fs/namespace.c:1318

task_work_run+0x1d4/0x260 kernel/task_work.c:233

exit_task_work include/linux/task_work.h:40 [inline]

do_exit+0x694/0x22f0 kernel/exit.c:971

do_group_exit+0x21c/0x2d0 kernel/exit.c:1112

__do_sys_exit_group kernel/exit.c:1123 [inline]

__se_sys_exit_group kernel/exit.c:1121 [inline]

__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1121

x64_sys_call+0x2210/0x2210 arch/x86/include/generated/asm/syscalls_64.h:232

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0xe8/0xf80 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x44f639

Code: Unable to access opcode bytes at 0x44f60f.

RSP: 002b:00007ffc15c4e088 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7

RAX: ffffffffffffffda RBX: 00000000004c32f0 RCX: 000000000044f639

RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000001

RBP: 0000000000000001 R08: ffffffffffffffc0 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004c32f0

R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001

</TASK>

Since rescue mount options will mark the full fs read-only, there should

be no new transaction triggered.

But during unmount we will evict all inodes, which can trigger a new

transaction, and triggers warnings on a heavily corrupted fs.

[CAUSE]

Btrfs allows new transaction even on a read-only fs, this is to allow

log replay happen even on read-only mounts, just like what ext4/xfs do.

However with rescue mount options, the fs is fully read-only and cannot

be remounted read-write, thus in that case we should also reject any new

transactions.

[FIX]

If we find the fs has rescue mount options, we should treat the fs as

error, so that no new transaction can be started.