Re: sys_chroot+sys_fchdir Fix

From: Al Viro
Date: Wed Sep 26 2007 - 23:59:54 EST

On Thu, Sep 27, 2007 at 02:01:37AM +0200, Adrian Bunk wrote:
> <-- snip -->
> Look, when chroot was being designed, I think they intended that even root
> should be unable to get out. They went so far as to say that dot-dot
> wouldn't let you out; and it doesn't.
> <-- snip -->
> You were clearly saying that whom you call "they" were the people who
> designed chroot. And it was you who was claiming in this statement that
> "they" said it.
> The OpenBSD manpage you quoted in this thread states chroot() was added
> in 4.2BSD, and 4.2BSD was released in 1983.
> You should therefore either bring a source where the people who designed
> chroot() in 1983 or earlier are stating what you claim they said or
> admit that you were talking utter bullshit.

chroot() is present in v7, thank you very much. /usr/sys/sys/sys4.c has


if (suser())

and back then it didn't stop lookups by .. at all - u_rdir is only used
in the beginning of namei() (when pathname starts with /), plus the obvious
refcounting in exit()/newproc(). So give me a break - back when it had
been introduced, it didn't do anything jail-like _at_ _all_.

That check appears only in BSD:
@@ -1,4 +1,4 @@
-/* vfs_lookup.c 4.4 03/06/81 */
+/* vfs_lookup.c 4.5 81/03/09 */

#include "../h/param.h"
#include "../h/systm.h"
@@ -107,6 +107,9 @@
u.u_segflg = 1;
eo = 0;
bp = NULL;
+ if (dp == u.u_rdir && u.u_dent.d_name[0] == '.' &&
+ u.u_dent.d_name[1] == '.' && u.u_dent.d_name[2] == 0)
+ goto cloop;


with spectaculary lousy commit message ("lint and a minor fixed") by
wnj. Feel free to ask Bill Joy WTF he had intended. At a guess,
more consistent behaviour in chrooted environment (i.e. pathname
resolution looking as if the subtree had been everything).

To talk about root-safety of _anything_ at that point is bloody ridiculous.
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