Originální popis anglicky:
setuid - set user identity
Návod, kniha: Linux Programmer's Manual
#include <sys/types.h>
#include <unistd.h>
int setuid(uid_t uid);
setuid sets the effective user ID of the current process. If the
effective userid of the caller is root, the real and saved user ID's are also
set.
Under Linux,
setuid is implemented like the POSIX version with the
_POSIX_SAVED_IDS feature. This allows a setuid (other than root) program to
drop all of its user privileges, do some un-privileged work, and then
re-engage the original effective user ID in a secure manner.
If the user is root or the program is setuid root, special care must be taken.
The
setuid function checks the effective user ID of the caller and if
it is the superuser, all process related user ID's are set to
uid.
After this has occurred, it is impossible for the program to regain root
privileges.
Thus, a setuid-root program wishing to temporarily drop root privileges, assume
the identity of a non-root user, and then regain root privileges afterwards
cannot use
setuid. You can accomplish this with the (non-POSIX, BSD)
call
seteuid.
On success, zero is returned. On error, -1 is returned, and
errno is set
appropriately.
- EAGAIN
- The uid does not match the current uid and
uid brings process over it's NPROC rlimit.
- EPERM
- The user is not privileged (Linux: does not have the
CAP_SETUID capability) and uid does not match the real or
saved user ID of the calling process.
SVr4, SVID, POSIX.1. Not quite compatible with the 4.4BSD call, which sets all
of the real, saved, and effective user IDs. SVr4 documents an additional
EINVAL error condition.
Linux has the concept of filesystem user ID, normally equal to the effective
user ID. The
setuid call also sets the filesystem user ID of the
current process. See
setfsuid(2).
If
uid is different from the old effective uid, the process will be
forbidden from leaving core dumps.
getuid(2),
seteuid(2),
setfsuid(2),
setreuid(2),
capabilities(7)
