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

[EXTENTLISTFREE] 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 ocfs2reflinkxattrinline(). 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 lcount 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.