squashfs: Fix stack overflow while symlink resolving

squashfs: Fix stack overflow while symlink resolving

The squashfs driver blindly follows symlinks, and calls sqfs_size()
recursively. So an attacker can create a crafted filesystem and with
a deep enough nesting level a stack overflow can be achieved.

Fix by limiting the nesting level to 8.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>