Re: [PATCH] ceph: fix possible null-pointer dereference in ceph_mdsmap_decode()

[Tuo Li]

Thanks for your feedback. It sounds good to put an "if (m->m_info)" around
the for loop to fix this bug, as well as avoid other potential bugs 
caused by calling
ceph_mdsmap_destroy(). I think we can prepare a V2 patch according to 
your advice.


On 2021/8/5 20:29, Jeff Layton wrote:
> On Thu, 2021-08-05 at 05:20 -0700, Tuo Li wrote:
> > kcalloc() is called to allocate memory for m->m_info, and if it fails,
> > ceph_mdsmap_destroy() behind the label out_err will be called:
> >    ceph_mdsmap_destroy(m);
> >
> > In ceph_mdsmap_destroy(), m->m_info is dereferenced through:
> >    kfree(m->m_info[i].export_targets);
> >
> > To fix this possible null-pointer dereference, if memory allocation
> > for m->m_info fails, free m and return -ENOMEM.
> >
> > Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>
> > Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
> > ---
> >   fs/ceph/mdsmap.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ceph/mdsmap.c b/fs/ceph/mdsmap.c
> > index abd9af7727ad..7d73e4b64b12 100644
> > --- a/fs/ceph/mdsmap.c
> > +++ b/fs/ceph/mdsmap.c
> > @@ -166,8 +166,10 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end, bool msgr2)
> >   	m->possible_max_rank = max(m->m_num_active_mds, m->m_max_mds);
> >   
> >   	m->m_info = kcalloc(m->possible_max_rank, sizeof(*m->m_info), GFP_NOFS);
> > -	if (!m->m_info)
> > -		goto nomem;
> > +	if (!m->m_info) {
> > +		kfree(m);
> > +		return ERR_PTR(-ENOMEM);
> > +	}
> >   
> >   	/* pick out active nodes from mds_info (state > 0) */
> >   	for (i = 0; i < n; i++) {
> Good catch. This function is already pretty complex. How about we
> instead fix this in ceph_mdsmap_destroy and make it safe to call that
> with the mdsmap in this state?
>
> Basically, just put an "if (m->m_info)" around the for loop in that
> function. Sound ok?