s390/decompressor: specify __decompress() buf len to avoid overflow
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.10.169 by commit 55dbd6f4ea954751340f4f73d5dcd7c8f12208b2. For more details please see the references link.