Re: [PATCH] ceph: quota: Fix invalid pointer access in

[Ilya Dryomov]

On Wed, Nov 15, 2023 at 2:17 PM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
>
>
> On 11/15/23 20:32, Ilya Dryomov wrote:
> > On Wed, Nov 15, 2023 at 1:35 AM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
> >>
> >> On 11/14/23 23:31, Wenchao Hao wrote:
> >>> This issue is reported by smatch, get_quota_realm() might return
> >>> ERR_PTR, so we should using IS_ERR_OR_NULL here to check the return
> >>> value.
> >>>
> >>> Signed-off-by: Wenchao Hao <haowenchao2@xxxxxxxxxx>
> >>> ---
> >>>    fs/ceph/quota.c | 2 +-
> >>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
> >>> index 9d36c3532de1..c4b2929c6a83 100644
> >>> --- a/fs/ceph/quota.c
> >>> +++ b/fs/ceph/quota.c
> >>> @@ -495,7 +495,7 @@ bool ceph_quota_update_statfs(struct ceph_fs_client *fsc, struct kstatfs *buf)
> >>>        realm = get_quota_realm(mdsc, d_inode(fsc->sb->s_root),
> >>>                                QUOTA_GET_MAX_BYTES, true);
> >>>        up_read(&mdsc->snap_rwsem);
> >>> -     if (!realm)
> >>> +     if (IS_ERR_OR_NULL(realm))
> >>>                return false;
> >>>
> >>>        spin_lock(&realm->inodes_with_caps_lock);
> >> Good catch.
> >>
> >> Reviewed-by: Xiubo Li <xiubli@xxxxxxxxxx>
> >>
> >> We should CC the stable mail list.
> > Hi Xiubo,
> >
> > What exactly is being fixed here?  get_quota_realm() is called with
> > retry=true, which means that no errors can be returned -- EAGAIN, the
> > only error that get_quota_realm() can otherwise generate, would be
> > handled internally by retrying.
>
> Yeah, that's true.
>
> > Am I missing something that makes this qualify for stable?
>
> Actually it's just for the smatch check for now.
>
> IMO we shouldn't depend on the 'retry', just potentially for new changes
> in future could return a ERR_PTR and cause potential bugs.

At present, ceph_quota_is_same_realm() also depends on it -- note how
old_realm isn't checked for errors at all and new_realm is only checked
for EAGAIN there.

>
> If that's not worth to make it for stable, let's remove it.

Yes, let's remove it.  Please update the commit message as well, so
that it's clear that this is squashing a static checker warning and
doesn't actually fix any immediate bug.

Thanks,

                Ilya