Messages in this thread | | | Date | Tue, 4 Mar 2008 15:45:00 -0600 | From | serge@hallyn ... | Subject | Re: CLONE_NEWNS and bind mounts to make "chroot" jail |
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Quoting Leibowitz, Michael (michael.leibowitz@intel.com): > If I understand correctly, the following should accomplish what I'm > looking for. However, pivot_root gives me EBUSY. I played around with > moving the mount --bind /jail /jail to before the unshared, as well as > making old_root a bind mount to itself. However, pivot_root always > seems to fail. Is there something obvious that I'm doing wrong? The
Yes, you cd /jail mount --bind /jail /jail pivot_root . old_root
but . is now mounted over.
-serge
> following is my test code (error checking has been removed for clarity, > except for pivot_root). > > char *newargv[]= { "sh", NULL }; > > chdir("/jail"); > unshare(CLONE_NEWNS)); > mount("/jail", "/jail", NULL, MS_BIND, NULL)); > mount("/bin", "bin", NULL, MS_BIND, NULL)); > mount("/usr", "usr", NULL, MS_BIND, NULL)); > mount("/lib", "lib", NULL, MS_BIND, NULL)); > if (pivot_root(".", "old_root")) perror("pivot_root . old_root"); > exec("./bash-static"); /* copied to /jail prior to running */ > > Thanks. > > >Serge replies: > [snip...snip] > >Try a few more things. Since you had entered /jail, you can view '/' > by > >looking at .. . But if you look at /, you dereference your > >task->fsroot. You never changed that, so it points to the original > >mount. If however you 'ls ..', you should see your 'jail' directory. > >However it won't have the /bin and /lib mounted because you didn't > > mount --rbind /jail / > >What you really want to do is > > mount --bind /jail /jail > >to make sure it's a mountpoint, then set up the new /jail using bind > >mounts like you're doing (and likely some rbinds in some places), then > >use pivot_root() to change your root. Then umount2("/old_root", > >MNT_DETACH). > > > >-serge > > -- > Michael Leibowitz > Software Engineer, UMG > Intel Corporation > michael.leibowitz at intel.com > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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