Description: vfs: fs_context: fix up param length parsing in legacy_parse_param
References:
 https://www.openwall.com/lists/oss-security/2022/01/18/7
 https://www.openwall.com/lists/oss-security/2022/01/25/14
 https://twitter.com/cor_ctf/status/1486022971034529794
 https://github.com/Crusaders-of-Rust/CVE-2022-0185
 https://www.willsroot.io/2022/01/cve-2022-0185.html
Notes:
 carnil> Introduced with 3e1aeb00e6d1 ("vfs: Implement a filesystem
 carnil> superblock creation/configuration context") in 5.1-rc1.
Bugs:
upstream: released (5.17-rc1) [722d94847de29310e8aa03fcbdb41fc92c521756]
5.10-upstream-stable: released (5.10.93) [eadde287a62e66b2f9e62d007c59a8f50d4b8413]
4.19-upstream-stable: N/A "Vulnerable code not present"
4.9-upstream-stable: N/A "Vulnerable code not present"
sid: released (5.15.15-1) [bugfix/all/vfs-fs_context-fix-up-param-length-parsing-in-legacy.patch]
5.10-bullseye-security: released (5.10.92-1) [bugfix/all/vfs-fs_context-fix-up-param-length-parsing-in-legacy.patch]
4.19-buster-security: N/A "Vulnerable code not present"
4.9-stretch-security: N/A "Vulnerable code not present"