Tribblix: manual page: issetugid.2

ISSETUGID(2) System Calls ISSETUGID(2)

NAME

issetugid - determine if current executable is running setuid or
setgid

SYNOPSIS

#include <unistd.h>

int issetugid(void);

DESCRIPTION

The issetugid() function enables library functions (in libtermlib,
libc, or other libraries) to guarantee safe behavior when used in
setuid or setgid programs or programs that run with more privileges
after a successful exec(2). Some library functions might be passed
insufficient information and not know whether the current program was
started setuid or setgid because a higher level calling code might
have made changes to the uid, euid, gid, or egid. These low-level
library functions are therefore unable to determine if they are being
run with elevated or normal privileges.

The issetugid() function should be used to determine if a path name
returned from a getenv(3C) call can be used safely to open the
specified file. It is often not safe to open such a file because the
status of the effective uid is not known.

The result of a call to issetugid() is unaffected by calls to
setuid(), setgid(), or other such calls. In case of a call to
fork(2), the child process inherits the same status.

The status of issetugid() is affected only by execve() (see exec(2)).
If a child process executes a new executable file, a new issetugid()
status will be based on the existing process's uid, euid, gid, and
egid permissions and on the modes of the executable file. If the new
executable file modes are setuid or setgid, or if the existing
process is executing the new image with uid != euid or gid != egid,
or if the permitted set before the call to the exec function is not a
superset of the inheritable set at that time, issetugid() returns 1
in the new process.

RETURN VALUES

The issetugid() function returns 1 if the process was made setuid or
setgid as the result of the last or a previous call to execve().
Otherwise it returns 0.

ERRORS

The issetugid() function is always successful. No return value is
reserved to indicate an error.