Vulnerability CVE-2024-46744
Published: 2024-09-18

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

Squashfs: sanity check symbolic link size

Syzkiller reports a "KMSAN: uninit-value in pick_link" bug.

This is caused by an uninitialised page, which is ultimately caused
by a corrupted symbolic link size read from disk.

The reason why the corrupted symlink size causes an uninitialised
page is due to the following sequence of events:

1. squashfs_read_inode() is called to read the symbolic
link from disk. This assigns the corrupted value
3875536935 to inode->i_size.

2. Later squashfs_symlink_read_folio() is called, which assigns
this corrupted value to the length variable, which being a
signed int, overflows producing a negative number.

3. The following loop that fills in the page contents checks that
the copied bytes is less than length, which being negative means
the loop is skipped, producing an uninitialised page.

This patch adds a sanity check which checks that the symbolic
link size is not larger than expected.

--

V2: fix spelling mistake.

 References:
https://git.kernel.org/stable/c/f82cb7f24032ed023fc67d26ea9bf322d8431a90
https://git.kernel.org/stable/c/1b9451ba6f21478a75288ea3e3fca4be35e2a438
https://git.kernel.org/stable/c/5c8906de98d0d7ad42ff3edf2cb6cd7e0ea658c4
https://git.kernel.org/stable/c/087f25b2d36adae19951114ffcbb7106ed405ebb
https://git.kernel.org/stable/c/fac5e82ab1334fc8ed6ff7183702df634bd1d93d
https://git.kernel.org/stable/c/c3af7e460a526007e4bed1ce3623274a1a6afe5e
https://git.kernel.org/stable/c/ef4e249971eb77ec33d74c5c3de1e2576faf6c90
https://git.kernel.org/stable/c/810ee43d9cd245d138a2733d87a24858a23f577d
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