open_as.c

[詳解]

/*++
/* NAME
/*  open_as 3
/* SUMMARY
/*  open file as user
/* SYNOPSIS
/*  #include <fcntl.h>
/*  #include <open_as.h>
/*
/*  int open_as(path, flags, mode, euid, egid)
/*  const char *path;
/*  int mode;
/*  uid_t   euid;
/*  gid_t   egid;
/* DESCRIPTION
/*  open_as() opens the named \fIpath\fR with the named \fIflags\fR
/*  and \fImode\fR, and with the effective rights specified by \fIeuid\fR
/*  and \fIegid\fR.  A -1 result means the open failed.
/* DIAGNOSTICS
/*  Fatal error: no permission to change privilege level.
/* SEE ALSO
/*  set_eugid(3) switch effective rights
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <fcntl.h>
#include <unistd.h>

/* Utility library. */

#include "msg.h"
#include "set_eugid.h"
#include "open_as.h"

/* open_as - open file as user */

int     open_as(const char *path, int flags, int mode, uid_t euid, gid_t egid)
{
    uid_t   saved_euid = geteuid();
    gid_t   saved_egid = getegid();
    int     fd;

    /*
     * Switch to the target user privileges.
     */
    set_eugid(euid, egid);

    /*
     * Open that file.
     */
    fd = open(path, flags, mode);

    /*
     * Restore saved privileges.
     */
    set_eugid(saved_euid, saved_egid);

    return (fd);
}