Re: [PATCH][CIFS] Fix uninitialized pointer access to dacl_ptr in build_sec_desc

[Steve French <smfrench@gmail.com>]

On Wed, Jun 23, 2021 at 6:41 AM Aurélien Aptel <aaptel@suse.com> wrote:
>
> Steve French <smfrench@gmail.com> writes:
>
> >     smb3: fix possible access to uninitialized pointer to DACL
> >
> >     dacl_ptr can be null so we must check for it (ie if dacloffset is
> > set) everywhere dacl_ptr is
> >     used in build_sec_desc - and we were missing one check
> >
> >     Addresses-Coverity: 1475598 ("Explicit null dereference")
>
> Looks OK since dacl_ptr is only set if dacloffset is set but it would
> be clearer if you check for dacl_ptr directly no? Any reason you are
> checking this way?
>
> I think this is clearer, unless I'm missing something:
>
> ndacl_ptr->num_aces = dacl_ptr ? dacl_ptr->num_aces : 0;

I agree that your suggestion is clearer but I was trying to match the
existing checks in the same code.
Will change both to your suggestion which is clearer.


> >
> >
> > --
> > Thanks,
> >
> > Steve
> > From ec06cb04376e5abc927a9b85dd768ce8728965bb Mon Sep 17 00:00:00 2001
> > From: Steve French <stfrench@microsoft.com>
> > Date: Tue, 22 Jun 2021 17:54:50 -0500
> > Subject: [PATCH] smb3: fix possible access to uninitialized pointer to DACL
> >
> > dacl_ptr can be null so we must check for it everywhere it is
> > used in build_sec_desc.
> >
> > Addresses-Coverity: 1475598 ("Explicit null dereference")
> > Signed-off-by: Steve French <stfrench@microsoft.com>
> > ---
> >  fs/cifs/cifsacl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
> > index 784407f9280f..25a8139336fa 100644
> > --- a/fs/cifs/cifsacl.c
> > +++ b/fs/cifs/cifsacl.c
> > @@ -1308,7 +1308,7 @@ static int build_sec_desc(struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd,
> >               ndacl_ptr = (struct cifs_acl *)((char *)pnntsd + ndacloffset);
> >               ndacl_ptr->revision =
> >                       dacloffset ? dacl_ptr->revision : cpu_to_le16(ACL_REVISION);
> > -             ndacl_ptr->num_aces = dacl_ptr->num_aces;
> > +             ndacl_ptr->num_aces = dacloffset ? dacl_ptr->num_aces : 0;
> >
> >               if (uid_valid(uid)) { /* chown */
> >                       uid_t id;
> > --
> > 2.30.2
> >
>
> --
> Aurélien Aptel / SUSE Labs Samba Team
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>


-- 
Thanks,

Steve