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Full Discussion: Create a program illustrating SUID
Top Forums Shell Programming and Scripting Create a program illustrating SUID Post 302788005 by Don Cragun on Sunday 31st of March 2013 09:00:20 PM
Old 03-31-2013
Quote:
Originally Posted by jim mcnamara
Code:
Many systems will clear the set-UID bit on a file when it is opened for writing

Per POSIX:

write() system call
Code:
Upon successful completion, where nbyte is greater than 0, 
write() will mark for update the st_ctime and st_mtime fields of the file, 
and if the file is a regular file, the S_ISUID and S_ISGID bits of the file 
mode may be cleared.

I don't see where open() does that - FWIW.
You're correct in saying that POSIX conforming systems aren't allowed to do this. (Although the standard isn't entirely consistent on this point. The descriptions of ftruncate() and truncate() both say that the S_ISUID and S_ISGID bits may be cleared if they change the size of the file. It is strange that open() with the O_TRUNC flag set doesn't make the same allowance.)

You may have also noticed the RATIONALE in the Base Definitions volume's description of the <sys/stat.h> header:
Quote:
The S_ISUID and S_ISGID bits may be cleared on any write, not just on open( ), as some historical implementations do.
I believe some non-conforming implementations still clear both of these bits on any successful open for writing, although I can't name any examples at this time.
 

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LEARN ABOUT DEBIAN

pidof

PIDOF(8)						Linux System Administrator's Manual						  PIDOF(8)

NAME

       pidof -- find the process ID of a running program.

SYNOPSIS

       pidof [-s] [-c] [-n] [-x] [-o omitpid[,omitpid..]]  [-o omitpid[,omitpid..]..]  program [program..]

DESCRIPTION

       Pidof  finds  the  process  id's (pids) of the named programs. It prints those id's on the standard output. This program is on some systems
       used in run-level change scripts, especially when the system has a System-V like rc structure. In that case these scripts  are  located	in
       /etc/rc?.d, where ? is the runlevel. If the system has a start-stop-daemon (8) program that should be used instead.

OPTIONS

       -s     Single shot - this instructs the program to only return one pid.

       -c     Only  return  process ids that are running with the same root directory.	This option is ignored for non-root users, as they will be
	      unable to check the current root directory of processes they do not own.

       -n     Avoid stat(2) system function call on all binaries which are located on network based file systems like NFS.  Instead of using  this
	      option the the variable PIDOF_NETFS may be set and exported.

       -x     Scripts too - this causes the program to also return process id's of shells running the named scripts.

       -o omitpid
	      Tells  pidof  to omit processes with that process id. The special pid %PPID can be used to name the parent process of the pidof pro-
	      gram, in other words the calling shell or shell script.

EXIT STATUS

       0      At least one program was found with the requested name.

       1      No program was found with the requested name.

NOTES

       pidof is actually the same program as killall5; the program behaves according to the name under which it is called.

       When pidof is invoked with a full pathname to the program it should find the pid of, it is reasonably safe. Otherwise it is  possible  that
       it  returns  pids  of  running programs that happen to have the same name as the program you're after but are actually other programs. Note
       that that the executable name of running processes is calculated with readlink(2), so symbolic links to executables will also match.

SEE ALSO

       shutdown(8), init(8), halt(8), reboot(8), killall5(8)

AUTHOR

       Miquel van Smoorenburg, miquels@cistron.nl

								    01 Sep 1998 							  PIDOF(8)
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