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diff --git a/lib/libsys/access.2 b/lib/libsys/access.2 new file mode 100644 index 000000000000..94a13dcc4dcf --- /dev/null +++ b/lib/libsys/access.2 @@ -0,0 +1,277 @@ +.\" 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. 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. +.\" +.Dd August 11, 2024 +.Dt ACCESS 2 +.Os +.Sh NAME +.Nm access , +.Nm eaccess , +.Nm faccessat +.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" +.Ft int +.Fn faccessat "int fd" "const char *path" "int mode" "int flag" +.Sh DESCRIPTION +The +.Fn access , +.Fn eaccess +and +.Fn faccessat +system calls report whether an attempt to access the file designated +by their +.Fa path +in the manner described by their +.Fa mode +argument is likely to succeed. +The value of +.Fa mode +is either the bitwise-inclusive OR of the desired permissions +.Po +.Dv R_OK +for read permission, +.Dv W_OK +for write permission, and +.Dv X_OK +for execute / search permission +.Pc +or +.Dv F_OK +to simply check whether the file exists. +.Pp +For a number of reasons, these system calls cannot be relied upon to +give a correct and definitive answer. +They can at best provide an early indication of the expected outcome, +to be confirmed by actually attempting the operation. +For existence checks, either +.Xr stat 2 +or +.Xr lstat 2 +should be used instead. +See also +.Sx SECURITY CONSIDERATIONS +below. +.Pp +The +.Fn eaccess +system call uses +the effective user ID and the group access list +to authorize the request; +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 +See the +.Sx DEFINITIONS +section of +.Xr intro 2 +for additional information on file access permissions and real +vs. effective user and group IDs. +.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 are performed using the effective user and group IDs, +like +.Fn eaccess , +instead of the real user and group ID, like +.Fn access . +.It Dv AT_RESOLVE_BENEATH +Only walk paths below the directory specified by the +.Ar fd +descriptor. +See the description of the +.Dv O_RESOLVE_BENEATH +flag in the +.Xr open 2 +manual page. +.It Dv AT_EMPTY_PATH +If the +.Fa path +argument is an empty string, operate on the file or directory +referenced by the descriptor +.Fa fd . +If +.Fa fd +is equal to +.Dv AT_FDCWD , +operate on the current working directory. +.It Dv AT_SYMLINK_NOFOLLOW +If +.Fa path +names a symbolic link, access of the symbolic link is evaluated. +.El +.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 +The +.Fn access , +.Fn eaccess , +and +.Fn faccessat +system calls may 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 +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 +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. +.It Bq Er EINTEGRITY +Corrupted data was detected while reading from 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 +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. +.It Bq Er ENOTCAPABLE +.Fa path +is an absolute path, +or contained a ".." component leading to a +directory outside of the directory hierarchy specified by +.Fa fd , +and the process is in capability mode. +.El +.Sh SEE ALSO +.Xr chmod 2 , +.Xr intro 2 , +.Xr stat 2 +.Sh STANDARDS +The +.Fn access +system call is expected to conform to +.St -p1003.1-90 . +The +.Fn faccessat +system call follows The Open Group Extended API Set 2 specification. +.Sh HISTORY +The +.Fn access +function appeared in +.At v7 . +The +.Fn faccessat +system call appeared in +.Fx 8.0 . +.Sh SECURITY CONSIDERATIONS +The +.Fn access , +.Fn eaccess , +and +.Fn faccessat +system calls are subject to time-of-check-to-time-of-use races and +should not be relied upon for file permission enforcement purposes. +Instead, applications should perform the desired action using the +requesting user's credentials. |