Re: [PATCH V5] squashfs: Add i_size check in squash_read_inode

[Al Viro <viro@xxxxxxxxxxxxxxxxxx>]

On Fri, Aug 02, 2024 at 07:16:40PM +0800, Lizhi Xu wrote:
> syzbot report KMSAN: uninit-value in pick_link, the root cause is that
> squashfs_symlink_read_folio did not check the length, resulting in folio
> not being initialized and did not return the corresponding error code.
> 
> The length is calculated from i_size, so it is necessary to add a check
> when i_size is initialized to confirm that its value is correct, otherwise
> an error -EINVAL will be returned. Strictly, the check only applies to the
> symlink type. Add larger symlink check.
> 
> Reported-and-tested-by: syzbot+24ac24ff58dc5b0d26b9@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=24ac24ff58dc5b0d26b9
> Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
> ---
>  fs/squashfs/inode.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/squashfs/inode.c b/fs/squashfs/inode.c
> index 16bd693d0b3a..6c5dd225482f 100644
> --- a/fs/squashfs/inode.c
> +++ b/fs/squashfs/inode.c
> @@ -287,6 +287,11 @@ int squashfs_read_inode(struct inode *inode, long long ino)
>  		inode->i_mode |= S_IFLNK;
>  		squashfs_i(inode)->start = block;
>  		squashfs_i(inode)->offset = offset;
> +		if ((int)inode->i_size < 0 || inode->i_size > PAGE_SIZE) {
> +			ERROR("Wrong i_size %d!\n", inode->i_size);
> +			return -EINVAL;
> +		}

ITYM something like
		if (le32_to_cpu(sqsh_ino->symlink_size) > PAGE_SIZE) {
			ERROR("Corrupted symlink\n");
			return -EINVAL;
		}