btrfs: avoid potential out-of-bounds in btrfs_encode_fh()

Overview

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

btrfs: avoid potential out-of-bounds in btrfs_encode_fh()

The function btrfs_encode_fh() does not properly account for the three cases it handles.

Before writing to the file handle (fh), the function only returns to the user BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or BTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes).

However, when a parent exists and the root ID of the parent and the inode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT (10 dwords, 40 bytes).

If *max_len is not large enough, this write goes out of bounds because BTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than BTRFS_FID_SIZE_CONNECTABLE originally returned.

This results in an 8-byte out-of-bounds write at fid->parent_root_objectid = parent_root_id.

A previous attempt to fix this issue was made but was lost.

https://lore.kernel.org/all/[email protected]/

Although this issue does not seem to be easily triggerable, it is a potential memory corruption bug that should be fixed. This patch resolves the issue by ensuring the function returns the appropriate size for all three cases and validates that *max_len is large enough before writing any data.

Affected

• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 60de2f55d2aca53e81b4ef2a67d7cc9e1eb677db
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 742b44342204e5dfe3926433823623c1a0c581df
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < d3a9a8e1275eb9b87f006b5562a287aea3f6885f
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < d91f6626133698362bba08fbc04bd72c466806d3
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 0276c8582488022f057b4cec21975a5edf079f47
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 361d67276eb8ec6be8f27f4ad6c6090459438fee
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 43143776b0a7604d873d1a6f3e552a00aa930224
• Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < dff4f9ff5d7f289e4545cc936362e01ed3252742
• Linux 2.6.29

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.