CVE-2024-49958

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

ocfs2: reserve space for inline xattr before attaching reflink tree

One of our customers reported a crash and a corrupted ocfs2 filesystem.
The crash was due to the detection of corruption. Upon troubleshooting,
the fsck -fn output showed the below corruption

[EXTENT_LIST_FREE] Extent list in owner 33080590 claims 230 as the next free chain record,
but fsck believes the largest valid value is 227. Clamp the next record value? n

The stat output from the debugfs.ocfs2 showed the following corruption
where the "Next Free Rec:" had overshot the "Count:" in the root metadata
block.

Inode: 33080590 Mode: 0640 Generation: 2619713622 (0x9c25a856)
FS Generation: 904309833 (0x35e6ac49)
CRC32: 00000000 ECC: 0000
Type: Regular Attr: 0x0 Flags: Valid
Dynamic Features: (0x16) HasXattr InlineXattr Refcounted
Extended Attributes Block: 0 Extended Attributes Inline Size: 256
User: 0 (root) Group: 0 (root) Size: 281320357888
Links: 1 Clusters: 141738
ctime: 0x66911b56 0x316edcb8 -- Fri Jul 12 06:02:30.829349048 2024
atime: 0x66911d6b 0x7f7a28d -- Fri Jul 12 06:11:23.133669517 2024
mtime: 0x66911b56 0x12ed75d7 -- Fri Jul 12 06:02:30.317552087 2024
dtime: 0x0 -- Wed Dec 31 17:00:00 1969
Refcount Block: 2777346
Last Extblk: 2886943 Orphan Slot: 0
Sub Alloc Slot: 0 Sub Alloc Bit: 14
Tree Depth: 1 Count: 227 Next Free Rec: 230
## Offset Clusters Block#
0 0 2310 2776351
1 2310 2139 2777375
2 4449 1221 2778399
3 5670 731 2779423
4 6401 566 2780447
....... .... .......
....... .... .......

The issue was in the reflink workfow while reserving space for inline
xattr. The problematic function is ocfs2_reflink_xattr_inline(). By the
time this function is called the reflink tree is already recreated at the
destination inode from the source inode. At this point, this function
reserves space for inline xattrs at the destination inode without even
checking if there is space at the root metadata block. It simply reduces
the l_count from 243 to 227 thereby making space of 256 bytes for inline
xattr whereas the inode already has extents beyond this index (in this
case up to 230), thereby causing corruption.

The fix for this is to reserve space for inline metadata at the destination
inode before the reflink tree gets recreated. The customer has verified the
fix.