Getting the Saved UID of a Process on OS X

If, like me, you were reading Setuid Demystified and thought "Wow, this is great, but it's got to work on OS X too, and there's no getresuid() or /proc/$pid/cred, so how do I use their proposed API?", then this code snippet is for you. It retrieves the saved set-user-id of a process on OS X, letting you populate the read_suid_from_X OS-specific function that's stubbed out in Chen and Wagner's code.

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>

int main()
{
        int retval, mib[4];
        struct kinfo_proc kp;
        size_t len;

        len = sizeof(kp);

        mib[0] = CTL_KERN;
        mib[1] = KERN_PROC;
        mib[2] = KERN_PROC_PID;
        mib[3] = getpid();

        retval = sysctl(mib, 4, &kp, &len, NULL, 0);
        if (retval == -1)
                return 1;

        if (len <= 0)
                return 2;

        printf("%u\n", kp.kp_eproc.e_pcred.p_svuid);

        return 0;
}

Technorati Tags: OSX, suid