linux-kernel - Re: [PATCH ghak21 V2 3/4] audit: add refused symlink to audit

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Message-ID: <20180313131347.726f12a0@ivy-bridge>
Date:   Tue, 13 Mar 2018 13:13:47 +0100
From:   Steve Grubb <sgrubb@...hat.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH ghak21 V2 3/4] audit: add refused symlink to audit_names

On Tue, 13 Mar 2018 06:52:51 -0400
Richard Guy Briggs <rgb@...hat.com> wrote:

> On 2018-03-13 11:38, Steve Grubb wrote:
> > On Tue, 13 Mar 2018 06:11:08 -0400
> > Richard Guy Briggs <rgb@...hat.com> wrote:
> >   
> > > On 2018-03-13 09:35, Steve Grubb wrote:  
> > > > On Mon, 12 Mar 2018 11:52:56 -0400
> > > > Richard Guy Briggs <rgb@...hat.com> wrote:
> > > >     
> > > > > On 2018-03-12 11:53, Paul Moore wrote:    
> > > > > > On Mon, Mar 12, 2018 at 11:26 AM, Richard Guy Briggs
> > > > > > <rgb@...hat.com> wrote:      
> > > > > > > On 2018-03-12 11:12, Paul Moore wrote:      
> > > > > > >> On Mon, Mar 12, 2018 at 2:31 AM, Richard Guy Briggs
> > > > > > >> <rgb@...hat.com> wrote:      
> > > > > > >> > Audit link denied events for symlinks had duplicate
> > > > > > >> > PATH records rather than just updating the existing
> > > > > > >> > PATH record. Update the symlink's PATH record with the
> > > > > > >> > current dentry and inode information.
> > > > > > >> >
> > > > > > >> > See:
> > > > > > >> > https://github.com/linux-audit/audit-kernel/issues/21
> > > > > > >> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com> ---
> > > > > > >> >  fs/namei.c | 1 +
> > > > > > >> >  1 file changed, 1 insertion(+)      
> > > > > > >>
> > > > > > >> Why didn't you include this in patch 4/4 like I asked
> > > > > > >> during the previous review?      
> > > > > > >
> > > > > > > Please see the last comment of:
> > > > > > > https://www.redhat.com/archives/linux-audit/2018-March/msg00070.html      
> > > > > > 
> > > > > > Yes, I just saw that ... I hadn't seen your replies on the
> > > > > > v1 patches until I had finished reviewing v2.  I just
> > > > > > replied to that mail in the v1 thread, but basically you
> > > > > > need to figure out what is necessary here and let us know.
> > > > > > If I have to figure it out it likely isn't going to get
> > > > > > done with enough soak time prior to the upcoming merge
> > > > > > window.      
> > > > > 
> > > > > Steve?  I was hoping you could chime in here.    
> > > > 
> > > > If the CWD record will always be the same as the PARENT record,
> > > > then we do not need the parent record. Duplicate information is
> > > > bad. Like all the duplicate SYSCALL information.    
> > > 
> > > The CWD record could be different from the PARENT record, since I
> > > could have SYMLINK=/tmp/test/symlink, CWD=/tmp, PARENT=/tmp/test.
> > > Does the parent record even matter since it might not be a
> > > directory operation like creat, unlink or rename?  
> > 
> > There's 2 issues. One is creating the path if what we have is
> > relative. In this situation CWD should be enough. But if the
> > question is whether the PARENT directory should be included...what
> > if the PARENT permissions do not allow the successful name
> > resolution? In that case we might only get a PARENT record no? In
> > that case we would need it.  
> 
> I think in the case of symlink creation, normal file create code path
> would be in effect, and would properly log parent and symlink source
> file paths (if a rule to log it was in effect) which is not something
> that would trigger a symlink link denied error.  Symlink link denied
> happens only when trying to actually follow the link before
> resolving the target path of a read/write/exec of the symlink target.
> 
> If the parent permissions of the link's target don't allow successful
> name resolution then the symlink link denied condition isn't met, but
> rather any other rule that applies to the target path.

Then I guess the PARENT record is not needed.

-Steve

> > > > > I'd just include it for completeness unless Steve thinks it
> > > > > will stand on its own and doesn't want the overhead.
> > > > >     
> > > > > > >> > diff --git a/fs/namei.c b/fs/namei.c
> > > > > > >> > index 50d2533..00f5041 100644
> > > > > > >> > --- a/fs/namei.c
> > > > > > >> > +++ b/fs/namei.c
> > > > > > >> > @@ -945,6 +945,7 @@ static inline int
> > > > > > >> > may_follow_link(struct nameidata *nd) if (nd->flags &
> > > > > > >> > LOOKUP_RCU) return -ECHILD;
> > > > > > >> >
> > > > > > >> > +       audit_inode(nd->name,
> > > > > > >> > nd->stack[0].link.dentry, 0);
> > > > > > >> > audit_log_link_denied("follow_link",
> > > > > > >> > &nd->stack[0].link); return -EACCES; }      
> > > > > > >>
> > > > > > >> paul moore      
> > > > > > >
> > > > > > > - RGB      
> > > > > > 
> > > > > > paul moore      
> > > > > 
> > > > > - RGB    
> > > 
> > > - RGB
> > > 
> > > --
> > > Richard Guy Briggs <rgb@...hat.com>
> > > Sr. S/W Engineer, Kernel Security, Base Operating Systems
> > > Remote, Ottawa, Red Hat Canada
> > > IRC: rgb, SunRaycer
> > > Voice: +1.647.777.2635, Internal: (81) 32635  
> >   
> 
> - RGB
> 
> --
> Richard Guy Briggs <rgb@...hat.com>
> Sr. S/W Engineer, Kernel Security, Base Operating Systems
> Remote, Ottawa, Red Hat Canada
> IRC: rgb, SunRaycer
> Voice: +1.647.777.2635, Internal: (81) 32635