Re: [PATCH] apparmor: Fix passt abstraction

["Maxime Bélair" <maxime.belair@canonical.com>]

On 5/17/24 14:28, Stefano Brivio wrote:

> Hi Maxime,

Hi Stefano,

> > Commit b686afa2 introduced the invalid apparmor rule `mount options=(rw, runbindable) /,` since runbindable mount rules cannot have a source.
> > Therefore running aa-logprof/aa-genprof will trigger errors (see https://bugs.launchpad.net/ubuntu/+source/apparmor/+bug/2065685)
> > 
> >     $ sudo aa-logprof
> >     ERROR: Operation {'runbindable'} cannot have a source. Source = AARE('/')
> 
> Oops, right, I didn't actually drop the source specification there. :(
> Thanks for fixing this.

After investigating this issue, I found that this bug stems from the following restriction not being implemented consistently in aa-* and apparmor_parser.

    $ man 2 mount
    
    If mountflags includes one of MS_SHARED, MS_PRIVATE, MS_SLAVE, or MS_UNBINDABLE [...] The source, and filesystemtype [...] arguments are ignored.

Therefore, your rule was valid for apparmor_parser, but not for aa-logprof/aa-genprof, as explained in https://bugs.launchpad.net/ubuntu/+source/apparmor/+bug/2065685 . I proposed a fix in https://gitlab.com/apparmor/apparmor/-/merge_requests/1236 .

> I wonder why I don't see this on Debian testing with AppArmor 3.0.13
> (same on openSUSE Tumbleweed).
> Is there something in particular I should do to reproduce/check this?

These new mount features have been added recently (https://gitlab.com/apparmor/apparmor/-/merge_requests/1153/diffs#b1394545ea32622b065c679b858c2ffd63f74480_0_116) : the bug can only be triggered by apparmor 4.0+ 

> > This patch fixes it to the intended behavior.
> > 
> > Signed-off-by: Maxime Bélair <maxime.belair@canonical.com>
> > ---
> >  contrib/apparmor/abstractions/passt | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/contrib/apparmor/abstractions/passt b/contrib/apparmor/abstractions/passt
> > index 61ec32c..d245115 100644
> > --- a/contrib/apparmor/abstractions/passt
> > +++ b/contrib/apparmor/abstractions/passt
> > @@ -26,7 +26,7 @@
> >    capability sys_ptrace,
> >  
> >    /					r,	# isolate_prefork(), isolation.c
> > -  mount options=(rw, runbindable) /,
> > +  mount options=(rw, runbindable) -> /,
> >    mount		""	-> "/",
> >    mount		""	-> "/tmp/",
> >    pivot_root	"/tmp/" -> "/tmp/",
> -- 
> Stefano