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setuid works but setgid fails with EPERM
Problem: The following code always fails saying "Error 1 setting group ID to nn" (where nn is the GID) if ( setuid((user).pw_uid) == -1) { printf("Error %d setting user ID to %d\n", errno, (user).pw_uid); return 1; } if ( setgid((user).pw_gid) == -1) { printf("Error %d setting group ID to %d\n", errno, (user).pw_gid); return 1; }
Solution: After the process has changed user id, it is no longer permitted to change group id. Simply swap the two, like this: if ( setgid((user).pw_gid) == -1) { printf("`Error %d setting group ID to %d\n`", errno, (user).pw_gid); return 1; } if ( setuid((user).pw_uid) == -1) { printf("`Error %d setting user ID to %d\n`", errno, (user).pw_uid); return 1; }
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