Describe CVE-2017-5551.
What is CVE-2017-5551?
The simple_set_acl function in fs/posix_acl.c in the Linux kernel before 4.9.6 preserves the setgid bit during a setxattr call involving a tmpfs filesystem, which allows local users to gain group privileges by leveraging the existence of a setgid program with restrictions on execute permissions.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-7097..