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

Reported-by: Xiang Mei <xmei5@asu.edu>
Link: https://lore.kernel.org/linux-btrfs/aik0hEV6ehKx6Ldv@Air.local/
Acked-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
[ Rebase, add a Link: tag, add an simple cause analyze ]
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: winmin

fs/btrfs/tree-checker.c

@@ -1923,6 +1923,12 @@ static int check_inode_ref(struct extent_buffer *leaf,
 
 		iref = (struct btrfs_inode_ref *)ptr;
 		namelen = btrfs_inode_ref_name_len(leaf, iref);
+		if (unlikely(namelen == 0 || namelen > BTRFS_NAME_LEN)) {
+			inode_ref_err(leaf, slot,
+				"invalid inode ref name length, has %u expect [1, %u]",
+				namelen, BTRFS_NAME_LEN);
+			return -EUCLEAN;
+		}
 		if (unlikely(ptr + sizeof(*iref) + namelen > end)) {
 			inode_ref_err(leaf, slot,
 				"inode ref overflow, ptr %lu end %lu namelen %u",