The patch titled Subject: Squashfs: sanity check symbolic link size has been added to the -mm mm-hotfixes-unstable branch. Its filename is squashfs-sanity-check-symbolic-link-size.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Phillip Lougher phillip@squashfs.org.uk Subject: Squashfs: sanity check symbolic link size Date: Sun, 11 Aug 2024 21:13:01 +0100

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 unitialised page.

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

Link: https://lkml.kernel.org/r/20240811201301.13076-1-phillip@squashfs.org.uk Signed-off-by: Phillip Lougher phillip@squashfs.org.uk Reported-by: Lizhi Xu lizhi.xu@windriver.com Reported-by: syzbot+24ac24ff58dc5b0d26b9@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000a90e8c061e86a76b@google.com/ Cc: Al Viro viro@zeniv.linux.org.uk Cc: Christian Brauner brauner@kernel.org Cc: Jan Kara jack@suse.cz Cc: Phillip Lougher phillip@squashfs.org.uk Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/squashfs/inode.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/squashfs/inode.c~squashfs-sanity-check-symbolic-link-size +++ a/fs/squashfs/inode.c @@ -279,8 +279,13 @@ int squashfs_read_inode(struct inode *in if (err < 0) goto failed_read;

- set_nlink(inode, le32_to_cpu(sqsh_ino->nlink)); inode->i_size = le32_to_cpu(sqsh_ino->symlink_size); + if (inode->i_size > PAGE_SIZE) { + ERROR("Corrupted symlink\n"); + return -EINVAL; + } + + set_nlink(inode, le32_to_cpu(sqsh_ino->nlink)); inode->i_op = &squashfs_symlink_inode_ops; inode_nohighmem(inode); inode->i_data.a_ops = &squashfs_symlink_aops; _

Patches currently in -mm which might be from phillip@squashfs.org.uk are

squashfs-sanity-check-symbolic-link-size.patch