Re: [PATCH] cifs: fix missing null session check in mount

[Shyam Prasad N <nspmangalore@gmail.com>]

On Wed, Jul 14, 2021 at 10:32 AM Steve French <smfrench@gmail.com> wrote:
>
> But isn't it the return from do_dfs_failover the issue ... we checked
> right before we called it on line 3561 ... but if it fails to populate
> ses ... then we break out of the loop - we could change it to "goto
> error" but the change in the patch is a little broader (wait until we
> exit the while loop)
>
Yes. That too.
We need to check return value from mount_get_conns and do_dfs_failover.
As Ronnie suggested, we need to make sure that when these functions
return error, none of the pointers get allocated.

> On Tue, Jul 13, 2021 at 11:54 PM Shyam Prasad N <nspmangalore@gmail.com> wrote:
> >
> > On Wed, Jul 14, 2021 at 6:19 AM Steve French <smfrench@gmail.com> wrote:
> > >
> > > Although it is unlikely to be have ended up with a null
> > > session pointer calling cifs_try_adding_channels in cifs_mount.
> > > Coverity correctly notes that we are already checking for
> > > it earlier (when we return from do_dfs_failover), so at
> > > a minimum to clarify the code we should make sure we also
> > > check for it when we exit the loop so we don't end up calling
> > > cifs_try_adding_channels or mount_setup_tlink with a null
> > > ses pointer.
> > >
> > > Addresses-Coverity: 1505608 ("Derefernce after null check")
> > > Reviewed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
> > > Signed-off-by: Steve French <stfrench@microsoft.com>
> > > ---
> > >  fs/cifs/connect.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> > > index db6c607269f5..463cae116c12 100644
> > > --- a/fs/cifs/connect.c
> > > +++ b/fs/cifs/connect.c
> > > @@ -3577,7 +3577,7 @@ int cifs_mount(struct cifs_sb_info *cifs_sb,
> > > struct smb3_fs_context *ctx)
> > >   rc = -ELOOP;
> > >   } while (rc == -EREMOTE);
> > >
> > > - if (rc || !tcon)
> > > + if (rc || !tcon || !ses)
> > >   goto error;
> > >
> > >   kfree(ref_path);
> > >
> > > --
> > > Thanks,
> > >
> > > Steve
> >
> > Hi Paulo,
> >
> > Doesn't it make sense to check rc, tcon and ses values right after
> > mount_get_conns call?
> >
> >         rc = mount_get_conns(ctx, cifs_sb, &xid, &server, &ses,
> > &tcon);          <<<<<<<<<<<<<<<<<<<
> >         /*
> >          * If called with 'nodfs' mount option, then skip DFS
> > resolving.  Otherwise unconditionally
> >          * try to get an DFS referral (even cached) to determine
> > whether it is an DFS mount.
> >          *
> >          * Skip prefix path to provide support for DFS referrals from
> > w2k8 servers which don't seem
> >          * to respond with PATH_NOT_COVERED to requests that include the prefix.
> >          */
> >         if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) ||
> >             dfs_cache_find(xid, ses, cifs_sb->local_nls,
> > cifs_remap(cifs_sb), ctx->UNC + 1, NULL,
> >                            NULL)) {
> >                 if (rc)
> >                         goto error;
> >                 /* Check if it is fully accessible and then mount it */
> >                 rc = is_path_remote(cifs_sb, ctx, xid, server, tcon);
> >                 if (!rc)
> >                         goto out;
> >                 if (rc != -EREMOTE)
> >                         goto error;
> >         }
> >
> > Why don't we check for all rc values that we don't expect, and call
> > dfs_cache_find only when it's an expected error?
> >
> > --
> > Regards,
> > Shyam
>
>
>
> --
> Thanks,
>
> Steve



-- 
Regards,
Shyam