Use snprintf instead of sprintf to avoid buffer overflows Use snprintf in uu_lockerr instead of lots of hardcoded constants and not null-terminated strncpy Return "" for OK and "device in use" for INUSE, it allows simple strcpy(buf, uu_lockerr(retcode)) without testing for special OK case (NULL was there) and obtaining meaningful result for INUSE ("" was there) without special testing for it too.
170 lines
4.5 KiB
Groff
170 lines
4.5 KiB
Groff
.\"
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.\" Copyright (c) 1996 Brian Somers <brian@awfulhak.demon.co.uk>
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.\"
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $Id: uucplock.3,v 1.3 1997/04/01 17:44:31 mpp Exp $
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.\" "
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.Dd March 30, 1997
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.Os
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.Dt uucplock 3
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.Sh NAME
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.Nm uu_lock ,
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.Nm uu_unlock ,
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.Nm uu_lockerr
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.Nd acquire and release control of a serial device
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.Sh SYNOPSIS
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.Fd #include <libutil.h>
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.Ft int
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.Fn uu_lock "char *ttyname"
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.Ft int
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.Fn uu_unlock "char *ttyname"
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.Ft char *
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.Fn uu_lockerr "int uu_lockresult"
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.Pp
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Link with
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.Va -lutil
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on the
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.Xr cc 1
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command line.
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.Sh DESCRIPTION
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The
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.Fn uu_lock
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function attempts to create a lock file called
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.Pa /var/spool/lock/LCK..
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with a suffix given by the passed
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.Fa ttyname .
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If the file already exists, it is expected to contain the process
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id of the locking program.
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.Pp
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If the file does not already exist, or the owning process given by
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the process id found in the lock file is no longer running,
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.Fn uu_lock
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will write its own process id into the file and return success.
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.Pp
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.Fn uu_unlock
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removes the lockfile created by
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.Fn uu_lock
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for the given
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.Fa ttyname .
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Care should be taken that
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.Fn uu_lock
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was successful before calling
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.Fn uu_unlock .
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.Pp
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.Fn uu_lockerr
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returns an error string representing the error
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.Fa uu_lockresult ,
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as returned from
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.Fn uu_lock .
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.Sh RETURN VALUES
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.Fn uu_unlock
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returns 0 on success and -1 on failure.
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.Pp
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.Fn uu_lock
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may return any of the following values:
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.Pp
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.Dv UU_LOCK_INUSE:
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The lock is in use by another process.
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.Pp
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.Dv UU_LOCK_OK:
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The lock was successfully created.
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.Pp
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.Dv UU_LOCK_OPEN_ERR:
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The lock file could not be opened via
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.Xr open 2 .
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.Pp
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.Dv UU_LOCK_READ_ERR:
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The lock file could not be read via
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.Xr read 2 .
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.Pp
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.Dv UU_LOCK_SEEK_ERR:
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The lock file was
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.Dq stale ,
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but the call to
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.Xr lseek 2
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necessary to write the current process id failed.
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.Pp
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.Dv UU_LOCK_WRITE_ERR:
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The current process id could not be written to the lock file via a call to
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.Xr write 2 .
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.Pp
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If a value of
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.Dv UU_LOCK_OK
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is passed to
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.Fn uu_lockerr ,
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an empty string returned.
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Otherwise, a string specifying
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the reason for failure is returned.
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.Fn uu_lockerr
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uses the current value of
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.Va errno
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to determine the exact error. Care should be made not to allow
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.Va errno
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to be changed between calls to
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.Fn uu_lock
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and
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.Fn uu_lockerr .
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.Sh ERRORS
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If
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.Fn uu_lock
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returns one of the four error values above, the global value
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.Va errno
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can be used to determine the cause. Refer to the respective manual pages
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for further details.
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.Pp
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.Fn uu_unlock
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will set the global variable
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.Va errno
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to reflect the reason that the lock file could not be removed.
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Refer to the description of
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.Xr unlink 2
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for further details.
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.Sh SEE ALSO
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.Xr open 2 ,
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.Xr read 2 ,
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.Xr lseek 2 ,
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.Xr write 2
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.Sh BUGS
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Locking is not atomic. Should a race condition occur, it's
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possible that the
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.Dq losing
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process fails to identify the
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.Dq winning
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process. If this happens,
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.Fn uu_lock
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returns
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.Dv UU_LOCK_READ_ERR
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and errno is set to
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.Er EINVAL .
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.Pp
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It is possible that a stale lock is not recognised as such if a new
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processes is assigned the same processes id as the program that left
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the stale lock.
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.Pp
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The calling process must have write permissions to the
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.Pa /var/spool/lock
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directory. There is no mechanism in place to ensure that the
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permissions of this directory are the same as those of the
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serial devices that might be locked.
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