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SETUID
!!!SETUID
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
LINUX-SPECIFIC REMARKS
SEE ALSO
----
!!NAME


setuid - set user identity
!!SYNOPSIS


__#include __
#include __


__int setuid(uid_t__ ''uid''__)__
!!DESCRIPTION


__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 uid 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__.
!!RETURN VALUE


On success, zero is returned. On error, -1 is returned, and
''errno'' is set appropriately.
!!ERRORS


__EPERM__


The user is not the super-user, and ''uid'' does not
match the real or saved user ID of the calling
process.
!!CONFORMING TO


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-SPECIFIC REMARKS


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.
!!SEE ALSO


getuid(2), setreuid(2), seteuid(2),
setfsuid(2)
----

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Last edited on Tuesday, June 4, 2002 12:23:46 am by "perry"

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