freebsd-dev/lib/libc/sys/access.2
Chris Costello de19436f24 Rename CAVEAT' to SECURITY CONSIDERATIONS' and move it up to
the correct location--this section consists solely of security
considerations information.

Sponsored by:	DARPA, NAI Labs
Obtained from:	TrustedBSD Project
2002-07-01 14:41:05 +00:00

159 lines
4.6 KiB
Groff

.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)access.2 8.2 (Berkeley) 4/1/94
.\" $FreeBSD$
.\"
.Dd September 21, 2001
.Dt ACCESS 2
.Os
.Sh NAME
.Nm access , eaccess
.Nd check accessibility of a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn access "const char *path" "int mode"
.Ft int
.Fn eaccess "const char *path" "int mode"
.Sh DESCRIPTION
The
.Fn access
and
.Fn eaccess
functions check the accessibility of the
file named by
the
.Fa path
argument
for the access permissions indicated by
the
.Fa mode
argument.
The value of
.Fa mode
is either the bitwise-inclusive OR of the access permissions to be
checked
.Dv ( R_OK
for read permission,
.Dv W_OK
for write permission, and
.Dv X_OK
for execute/search permission),
or the existence test
.Pq Dv F_OK .
.Pp
For additional information, see the
.Sx "File Access Permission"
section of
.Xr intro 2 .
.Pp
The
.Fn eaccess
call uses
the effective user ID and the group access list
to authorize the request;
the
.Fn access
call uses
the real user ID in place of the effective user ID,
the real group ID in place of the effective group ID,
and the rest of the group access list.
.Pp
Even if a process's real or effective user has appropriate privileges
and indicates success for
.Dv X_OK ,
the file may not actually have execute permission bits set.
Likewise for
.Dv R_OK
and
.Dv W_OK .
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
Access to the file is denied if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EROFS
Write access is requested for a file on a read-only file system.
.It Bq Er ETXTBSY
Write access is requested for a pure procedure (shared text)
file presently being executed.
.It Bq Er EACCES
Permission bits of the file mode do not permit the requested
access, or search permission is denied on a component of the
path prefix.
.It Bq Er EFAULT
.Fa path
points outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SECURITY CONSIDERATIONS
The
.Fn access
call
is a potential security hole due to race conditions and
should never be used.
Set-user-ID and set-group-ID applications should restore the
effective user or group ID,
and perform actions directly rather than use
.Fn access
to simulate access checks for the real user or group ID.
The
.Fn eaccess
call
likewise may be subject to races if used inappropriately.
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr intro 2 ,
.Xr stat 2
.Sh STANDARDS
The
.Fn access
function call is expected to conform to
.St -p1003.1-90 .
.Sh HISTORY
An
.Fn access
function call appeared in
.At v7 .