-.\" $NetBSD: access.2,v 1.7 1995/02/27 12:31:44 cgd Exp $
-.\"
.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" 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.
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.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\" SUCH DAMAGE.
.\"
.\" @(#)access.2 8.2 (Berkeley) 4/1/94
+.\" $FreeBSD$
.\"
-.Dd April 1, 1994
+.Dd September 15, 2014
.Dt ACCESS 2
-.Os BSD 4
+.Os
.Sh NAME
-.Nm access
-.Nd check access permissions of a file or pathname
+.Nm access ,
+.Nm faccessat
+.Nd check accessibility of a file
.Sh SYNOPSIS
-.Fd #include <unistd.h>
+.In unistd.h
.Ft int
.Fn access "const char *path" "int mode"
+.Ft int
+.Fn faccessat "int fd" "const char *path" "int mode" "int flag"
.Sh DESCRIPTION
The
.Fn access
-function checks the accessibility of the
+system call checks the accessibility of the
file named by
+the
.Fa path
+argument
for the access permissions indicated by
-.Fa mode .
+the
+.Fa mode
+argument.
The value of
.Fa mode
-is the bitwise inclusive OR of the access permissions to be
+is either the bitwise-inclusive OR of the access permissions to be
checked
-.Pf ( Dv R_OK
+.Dv ( R_OK
for read permission,
.Dv W_OK
-for write permission and
+for write permission, and
.Dv X_OK
-for execute/search permission) or the existence test,
-.Dv F_OK .
-All components of the pathname
-.Fa path
-are checked for access permissions (including
-.Dv F_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 real user ID is used in place of the effective user ID
-and the real group access list
-(including the real group ID) are
-used in place of the effective ID for verifying permission.
+The
+.Fn access
+system 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
+The
+.Fn faccessat
+system call is equivalent to
+.Fn access
+except in the case where
+.Fa path
+specifies a relative path.
+In this case the file whose accessibility is to be determined is
+located relative to the directory associated with the file descriptor
+.Fa fd
+instead of the current working directory.
+If
+.Fn faccessat
+is passed the special value
+.Dv AT_FDCWD
+in the
+.Fa fd
+parameter, the current working directory is used and the behavior is
+identical to a call to
+.Fn access .
+Values for
+.Fa flag
+are constructed by a bitwise-inclusive OR of flags from the following
+list, defined in
+.In fcntl.h :
+.Bl -tag -width indent
+.It Dv AT_EACCESS
+The checks for accessibility are performed using the effective user and group
+IDs instead of the real user and group ID as required in a call to
+.Fn access .
+.El
.Pp
Even if a process has appropriate privileges and indicates success for
.Dv X_OK ,
and
.Dv W_OK .
.Sh RETURN VALUES
-If
-.Fa path
-cannot be found or if any of the desired access modes would
-not be granted, then a -1 value is returned; otherwise
-a 0 value is returned.
+.Rv -std
.Sh ERRORS
-Access to the file is denied if:
+.Fn access
+or
+.Fn faccessat
+will fail if:
.Bl -tag -width Er
+.It Bq Er EINVAL
+The value of the
+.Fa mode
+argument is invalid.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
.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. The owner of a file has permission checked with
-respect to the ``owner'' read, write, and execute mode bits,
-members of the file's group other than the owner have permission
-checked with respect to the ``group'' mode bits, and all
-others have permissions checked with respect to the ``other''
-mode bits.
+path prefix.
.It Bq Er EFAULT
-.Fa Path
+The
+.Fa path
+argument
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
+.Pp
+Also, the
+.Fn faccessat
+system call may fail if:
+.Bl -tag -width Er
+.It Bq Er EBADF
+The
+.Fa path
+argument does not specify an absolute path and the
+.Fa fd
+argument is
+neither
+.Dv AT_FDCWD
+nor a valid file descriptor.
.It Bq Er EINVAL
-An invalid value was specified for
-.Ar mode .
+The value of the
+.Fa flag
+argument is not valid.
+.It Bq Er ENOTDIR
+The
+.Fa path
+argument is not an absolute path and
+.Fa fd
+is neither
+.Dv AT_FDCWD
+nor a file descriptor associated with a directory.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
+.Xr intro 2 ,
.Xr stat 2
.Sh STANDARDS
The
.Fn access
-function conforms to
+system call is expected to conform to
.St -p1003.1-90 .
-.Sh CAVEAT
-.Fn Access
-is a potential security hole and
-should never be used.
+The
+.Fn faccessat
+system call is expected to conform to POSIX.1-2008 .
+.Sh HISTORY
+The
+.Fn access
+function appeared in
+.At v7 .
+.Sh SECURITY CONSIDERATIONS
+The result of
+.Fn access
+should not be used to make an actual access control decision, since its
+response, even if correct at the moment it is formed, may be outdated at the
+time you act on it.
+.Fn access
+results should only be used to pre-flight, such as when configuring user
+interface elements or for optimization purposes. The actual access control
+decision should be made by attempting to execute the relevant system call while
+holding the applicable credentials, and properly handling any resulting errors;
+and this must be done even though
+.Fn access
+may have predicted success.
+.Pp
+Additionally, 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.
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