> I was reading that some programs setuid themselves to root to do things (I
> think mount -all can be made to do it?). What are the restrictions of this?
> How are malicious (or stupid) programs prevented from root-ing themselves
> and causing Bad Things to happen?
An arbitrary program can't make itself root; this capability has to be
set up by the root user first. The mechanism is the "Set Effective
User-ID or Group-ID on Execution bit - if this is activated "chmod u+s"
on an executable file, then whenever that file is executed, the
"effective user ID" of the executing process will be set to the same as
the file's owner. Thus, for example, the mount command always runs "as
root", so that it can make the necessary system calls to mount a fs.
Only the file's owner (or root) can turn on the seteuid bit of a file.
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colm at tuatha.org (personal) | colm.buckley at nwcgroup.com (business)
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