CVE-2026-98959

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

btrfs: fix xattr replace when multiple xattrs are packed in the same item

If we have a btrfs dir item item that packs multiple xattrs and then we replace the value of one of them (with the setxattr(2) family of syscalls) with another value of a different size, we end up not having a fully initialized btrfs dir item, resulting in a corruption that the tree checker will detect at extent buffer writeback time.

This is because in btrfs setxattr() when we find a btrfs dir item with multiple xattrs (due to the crc32c hash of their name being the same) we delete one of the xattr items (btrfs dir item) and then insert a new one, but the deletion and insertion results in shifting existing data in the leaf and therefore when the new value of a xattr has a different size, the new btrfs dir item is placed in a leaf section that was not initialized and we only copy the value's data and set the value's length in the new btrfs dir item, without setting the name, the name's length, the key (which must be all zeroes for xattrs), flags (BTRFS FT XATTR) and transaction ID.

The following script reproduces the issue:

$ cat test.sh #!/bin/bash

DEV=/dev/sdi MNT=/mnt/sdi

mkfs.btrfs -f $DEV mount $DEV $MNT

touch $MNT/testfile

setfattr -n user.foobar -v 123 $MNT/testfile setfattr -n user.WvG1c1Td -v qwerty $MNT/testfile

echo "xattrs before:" getfattr --absolute-names --dump $MNT/testfile

setfattr -n user.foobar -v abcdefghijklmnopqrstuvwxyz $MNT/testfile

echo "xattrs after:" getfattr --absolute-names --dump $MNT/testfile

umount $MNT

Running it:

$ ./test.sh (...) xattrs before:

user.WvG1c1Td="qwerty" user.foobar="123"

xattrs after:

user.WvG1c1Td="qwerty"

So the "user.foobar" xattr is missing and there was a transaction abort when unmounting the fs with the following traces in dmesg:

$ dmesg [869800.159271] BTRFS warning (device sdi): access to eb bytenr 30474240 len 16384 out of range start 16015 len 25964 [869800.159293] ------------[ cut here ]------------ [869800.159296] WARNING: fs/btrfs/extent io.c:4408 at report eb range+0x44/0x60 [btrfs], CPU#8: getfattr/2605179 [869800.168961] Modules linked in: btrfs dm thin pool (...) [869800.190527] CPU: 8 UID: 0 PID: 2605179 Comm: getfattr Tainted: G W 7.3.0-rc3-btrfs-next-244+ #1 PREEMPT(full) [869800.193726] Tainted: [W]=WARN [869800.194502] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [869800.197576] RIP: 0010:report eb range+0x44/0x60 [btrfs] [869800.198985] Code: 48 8b 7b 18 (...) [869800.203531] RSP: 0018:ffffce4541937d58 EFLAGS: 00010246 [869800.204609] RAX: 0000000000000000 RBX: ffff8dde054b8738 RCX: 0000000000000000 [869800.206137] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffc04c92a0 [869800.207645] RBP: 0000000000003e8f R08: 0000000000000000 R09: 3fffffffffefffff [869800.226175] R10: ffffce4541937a88 R11: 0000000000000003 R12: 000000000000656c [869800.227594] R13: ffff8dde14be800f R14: 000000000000656c R15: 0000000000000069 [869800.229097] FS: 00007f59023bb780(0000) GS:ffff8de5788ed000(0000) knlGS:0000000000000000 [869800.231137] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [869800.232321] CR2: 0000558dc45e6a78 CR3: 0000000765b16004 CR4: 0000000000370ef0 [869800.233783] Call Trace: [869800.234330] [869800.234791] read extent buffer+0x4d/0x100 [btrfs] [869800.235898] btrfs listxattr+0x199/0x240 [btrfs] [869800.236912] vfs listxattr+0x51/0 ---truncated---