CVE-2026-46160: btrfs: fix missing last_unlink_trans update when removing a directory
In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix missing last_unlink_trans update when removing a directory

When removing a directory we are not updating its last_unlink_trans field,
which can result in incorrect fsync behaviour in case some one fsyncs the
directory after it was removed because it's holding a file descriptor on
it.

Example scenario:

   mkdir /mnt/dir1
   mkdir /mnt/dir1/dir2
   mkdir /mnt/dir3

   sync -f /mnt

   # Do some change to the directory and fsync it.
   chmod 700 /mnt/dir1
   xfs_io -c fsync /mnt/dir1

   # Move dir2 out of dir1 so that dir1 becomes empty.
   mv /mnt/dir1/dir2 /mnt/dir3/

   open fd on /mnt/dir1
   call rmdir(2) on path "/mnt/dir1"
   fsync fd

   <trigger power failure>

When attempting to mount the filesystem, the log replay will fail with
an -EIO error and dmesg/syslog has the following:

   [445771.626482] BTRFS info (device dm-0): first mount of filesystem 0368bbea-6c5e-44b5-b409-09abe496e650
   [445771.626486] BTRFS info (device dm-0): using crc32c checksum algorithm
   [445771.627912] BTRFS info (device dm-0): start tree-log replay
   [445771.628335] page: refcount:2 mapcount:0 mapping:0000000061443ddc index:0x1d00 pfn:0x7072a5
   [445771.629453] memcg:ffff89f400351b00
   [445771.629892] aops:btree_aops [btrfs] ino:1
   [445771.630737] flags: 0x17fffc00000402a(uptodate|lru|private|writeback|node=0|zone=2|lastcpupid=0x1ffff)
   [445771.632359] raw: 017fffc00000402a fffff47284d950c8 fffff472907b7c08 ffff89f458e412b8
   [445771.633713] raw: 0000000000001d00 ffff89f6c51d1a90 00000002ffffffff ffff89f400351b00
   [445771.635029] page dumped because: eb page dump
   [445771.635825] BTRFS critical (device dm-0): corrupt leaf: root=5 block=30408704 slot=10 ino=258, invalid nlink: has 2 expect no more than 1 for dir
   [445771.638088] BTRFS info (device dm-0): leaf 30408704 gen 10 total ptrs 17 free space 14878 owner 5
   [445771.638091] BTRFS info (device dm-0): refs 4 lock_owner 0 current 3581087
   [445771.638094] 	item 0 key (256 INODE_ITEM 0) itemoff 16123 itemsize 160
   [445771.638097] 		inode generation 3 transid 9 size 16 nbytes 16384
   [445771.638098] 		block group 0 mode 40755 links 1 uid 0 gid 0
   [445771.638100] 		rdev 0 sequence 2 flags 0x0
   [445771.638102] 		atime 1775744884.0
   [445771.660056] 		ctime 1775744885.645502983
   [445771.660058] 		mtime 1775744885.645502983
   [445771.660060] 		otime 1775744884.0
   [445771.660062] 	item 1 key (256 INODE_REF 256) itemoff 16111 itemsize 12
   [445771.660064] 		index 0 name_len 2
   [445771.660066] 	item 2 key (256 DIR_ITEM 1843588421) itemoff 16077 itemsize 34
   [445771.660068] 		location key (259 1 0) type 2
   [445771.660070] 		transid 9 data_len 0 name_len 4
   [445771.660075] 	item 3 key (256 DIR_ITEM 2363071922) itemoff 16043 itemsize 34
   [445771.660076] 		location key (257 1 0) type 2
   [445771.660077] 		transid 9 data_len 0 name_len 4
   [445771.660078] 	item 4 key (256 DIR_INDEX 2) itemoff 16009 itemsize 34
   [445771.660079] 		location key (257 1 0) type 2
   [445771.660080] 		transid 9 data_len 0 name_len 4
   [445771.660081] 	item 5 key (256 DIR_INDEX 3) itemoff 15975 itemsize 34
   [445771.660082] 		location key (259 1 0) type 2
   [445771.660083] 		transid 9 data_len 0 name_len 4
   [445771.660084] 	item 6 key (257 INODE_ITEM 0) itemoff 15815 itemsize 160
   [445771.660086] 		inode generation 9 transid 9 size 8 nbytes 0
   [445771.660087] 		block group 0 mode 40777 links 1 uid 0 gid 0
   [445771.660088] 		rdev 0 sequence 2 flags 0x0
   [445771.660089] 		atime 1775744885.641174097
   [445771.660090] 		ctime 1775744885.645502983
   [445771.660091] 		mtime 1775744885.645502983
   [445771.660105] 		otime 1775744885.641174097
   [445771.660106] 	item 7 key (257 INODE_REF 256) itemoff 15801 itemsize 14
   [445771.660107] 		index 2 name_len 4
   [445771.660108] 	item 8 key (257 DIR_ITEM 2676584006) itemoff 15767 itemsize 34
   [445771.660109] 		location key (2
---truncated---
CVSS v3.1: 5.5