leo@marco.UUCP (Matthias Pfaller) (07/27/90)
Yesterday I tried to use chroot(2).
my program looked like this
main()
{
chroot("/mnt");
execl("/bin/sh", "sh", (char *)0);
}
The program worked, and I had a sh with a changed root-directory.
but:
1. I could do a "cd /; cd .." and I was in the former root-directory
is this behaviour correct?
2. The shell could no longer find commands. For example I could do
'ls -l /bin/ls' and ls is found and displays /bin/ls.
The displayed ls is that from /mnt/bin/ls, but the loaded one is
that from the former /bin/ls. If I tried to start a program from
/usr/bin (actually /mnt/usr/bin) the exec failed. I think the problem
is, that mm only changes to the exec'ing process workingdirectory, but
does not also change it's rootdirectory.
Has anyone fixed this allready?
Matthias Pfaller (leo@verw.marco.de)brucee@runxtsa.runx.oz.au (Bruce Evans) (08/05/90)
In article <441@alice.marco.UUCP> leo@marco.UUCP (Matthias Pfaller) writes: >1. I could do a "cd /; cd .." and I was in the former root-directory > is this behaviour correct? No. I think it will suffice to not follow the ".." link when the current dicrectory is the root directory. >2. [old binaries can still be executed] > I think the problem > is, that mm only changes to the exec'ing process workingdirectory, but > does not also change it's rootdirectory. Yes. MM does a tell_fs(CHDIR, ...) to change the working directory. do_chdir() in FS is kludged to switch from MM's workdir to the user's workdir (and back) when called by MM. It also switches the effective uid, but not the rootdir. I started to add code to switch to the user's rootdir but stopped after realizing that this would zap the method of switching back the workdir (by setting MM's workdir = MM's rootdir). But perhaps MM doesn't need a workdir of its own. The kludges are needed because MM is a server and the user task is not visible to FS. Doing it "right" would require a lot of extra system calls like special_open(user_nr, filename, mode), or overloading the bits in the arguments as is already done for read() :-(. -- Bruce Evans Internet: brucee@runxtsa.runx.oz.au UUCP: uunet!runxtsa.runx.oz.au!brucee (My other address (evans@ditsyda.oz.au) no longer works)