Re: [RFC PATCH ghak21 4/4] audit: add parent of refused symlink to audit_names

[Richard Guy Briggs]

On 2018-02-15 18:34, Paul Moore wrote:
> On Wed, Feb 14, 2018 at 11:18 AM, Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> > Audit link denied events for symlinks were missing the parent PATH
> > record.  Add it.  Since the full pathname may not be available,
> > reconstruct it from the path in the nameidata supplied.
> >
> > See: https://github.com/linux-audit/audit-kernel/issues/21
> > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > ---
> >  fs/namei.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/fs/namei.c b/fs/namei.c
> > index 0edf133..bf1c046b 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -923,6 +923,7 @@ static inline int may_follow_link(struct nameidata *nd)
> >         const struct inode *inode;
> >         const struct inode *parent;
> >         kuid_t puid;
> > +       char *pathname;
> >
> >         if (!sysctl_protected_symlinks)
> >                 return 0;
> > @@ -945,6 +946,14 @@ static inline int may_follow_link(struct nameidata *nd)
> >         if (nd->flags & LOOKUP_RCU)
> >                 return -ECHILD;
> >
> > +       pathname = kmalloc(PATH_MAX + 1, GFP_KERNEL);
> > +       if (!pathname)
> > +               return -ENOMEM;
> > +       audit_inode(getname_kernel(d_absolute_path(&nd->stack[0].link, pathname,
> > +                                                  PATH_MAX + 1)),
> > +                   nd->stack[0].link.dentry, 0);
> 
> Hmm, it's been a while since I've looked at the audit vfs/inode code,
> but isn't the audit_inode() call directly above effectively a
> duplicate of the audit_inode(nd->name, nd->stack[0].link.dentry, 0)
> call you added in patch 3/4?

It gets the full pathname string of the link, then converts it to a
struct filename*, and then below, we feed it that struct filename* with
the parent's dentry and the LOOKUP_PARENT flag to drop the last part of
the pathname and set the filetype to PARENT.

I didn't try, it, but I expect if I feed it parent's dentry above, I'd
get only the parent pathname and when I feed it to audit_inode() below
it would again drop the last part of the pathname when the LOOKUP_PARENT
flag is included, or not label it as a filetype PARENT if we don't
include the flag to get the full parent pathname.

> > +       audit_inode(nd->name, nd->stack[0].link.dentry->d_parent, LOOKUP_PARENT);
> > +
> >         audit_inode(nd->name, nd->stack[0].link.dentry, 0);
> >         audit_log_link_denied("follow_link", &nd->stack[0].link);
> >         return -EACCES;
> > --
> > 1.8.3.1
> 
> -- 
> paul moore
> www.paul-moore.com
> 
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- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
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