CVE-2026-93813

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

btrfs: tree-checker: validate INODE_REF's namelen

[BUG]

A crafted btrfs image can trigger the following crash:

BUG: unable to handle page fault for address: ffffd1dc42884000

#PF: supervisor write access in kernel mode

#PF: error_code(0x0002) - not-present page

CPU: 9 UID: 0 PID: 1034 Comm: poc Not tainted 7.1.0-rc4-custom+ #383 PREEMPT(full) 46af0a92938a63be7132e0dfd71e62327c51d5c2

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022

RIP: 0010:memcpy+0xc/0x10

Call Trace:

<TASK>

read_extent_buffer+0xe4/0x100 [btrfs 3cf0785dd58fec8c5ff84633b772f17ce1f92a8f]

btrfs_get_name+0x15e/0x1e0 [btrfs 3cf0785dd58fec8c5ff84633b772f17ce1f92a8f]

reconnect_path+0x165/0x390

exportfs_decode_fh_raw+0x337/0x400

? drop_caches_sysctl_handler+0xb0/0xb0

</TASK>

---[ end trace 0000000000000000 ]---

RIP: 0010:memcpy+0xc/0x10

Kernel panic - not syncing: Fatal exception

[CAUSE]

TThe crafted image has the following corrupted INODE_REF item:

item 9 key (258 INODE_REF 257) itemoff 11544 itemsize 4106

index 2 namelen 4096 name: d\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000

The itemsize matches the namelen, but the namelen is 4096, way larger

than normal name length limit (BTRFS_NAME_LEN, 255).

Meanwhile the memory of the @name is only 255 byte sized, this will cause

out-of-boundary access, and cause the above crash.

[FIX]

Add extra namelen verification for INODE_REF, just like what we have

done in ROOT_REF checks.

Now the crafted image can be rejected gracefully:

BTRFS critical (device dm-2): corrupt leaf: root=5 block=30572544 slot=14 ino=259, invalid inode ref name length, has 4096 expect [1, 255]

BTRFS error (device dm-2): read time tree block corruption detected on logical 30572544 mirror 2

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