Security Strategies in Linux Platforms and Applications, 3rd Edition

Regular and Special Permissions

Linux files and directories have a user and a group owner. Permissions are split into three groups: the user who owns the file, the users in the group that owns the file, and all other users.

Regular permissions are read, write, and execute. Special permissions go beyond execute bits and can extend the executable permissions. In general, these special permissions, especially the set user ID (SUID) bit, may be a security risk. (The SUID bit is a special permission that allows others to execute the given file with the rights of the user owner of the file.) If there’s a binary that’s vulnerable to the ptrace system call, however, the SUID or SGID bit may stop that system call in its tracks, preventing an unauthorized ...