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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

vmware-user-suid-wrapper

VMWARE-USER-SUID-WRAPPER(8)					   Open VM Tools				       VMWARE-USER-SUID-WRAPPER(8)

NAME

       vmware-user-suid-wrapper - wrapper programm for vmware-user(1)

SYNOPSIS

       vmware-user-suid-wrapper

DESCRIPTION

       Operations  on  the  vmblock(9) filesystem are considered privileged, and as such may only be issued on a file descriptor acquired by root.
       This is accomplished by vmware-user-suid-wrapper, a small setuid wrapper whose only purpose is to acquire  a  filesystem  file  descriptor,
       drop  superuser	privileges, and then execute vmware-user(1).  In particular, prepare the system for vmware-user means that it unmounts the
       vmblock file system, unloads the vmblock module, then reloads the module, mounts the file system, and opens a file descriptor that  vmware-
       user can use to add and remove blocks.

OPTIONS

       vmware-user-suid-wrapper has no options.

SEE ALSO

       vmware-checkvm(1)
       vmware-hgfsclient(1)
       vmware-toolbox(1)
       vmware-toolbox-cmd(1)
       vmware-user(1)
       vmware-xferlogs(1)
       libguestlib(3)
       libvmtools(3)
       vmware-guestd(8)
       vmware-hgfsmounter(8)
       vmblock(9)
       vmci(9)
       vmhgfs(9)
       vmmemctl(9)
       vmsock(9)
       vmsync(9)
       vmxnet(9)
       vmxnet3(9)

HOMEPAGE

       More information about vmware-user-suid-wrapper and the Open VM Tools can be found at <http://open-vm-tools.sourceforge.net/>.

AUTHOR

       Open VM Tools were written by VMware, Inc. <http://www.vmware.com/>.

       This  manual  page  was	put  together from homepage materials by Daniel Baumann <daniel.baumann@progress-technologies.net>, for the Debian
       project (but may be used by others).

2010.03.20-243334						    2010-04-08					       VMWARE-USER-SUID-WRAPPER(8)
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