linux-kernel - Re: [PATCH] ceph: fix possible null-pointer dereference in ceph_mdsmap

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Date:   Thu, 05 Aug 2021 08:29:30 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Tuo Li <islituo@...il.com>, idryomov@...il.com
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju1990@...il.com, TOTE Robot <oslab@...nghua.edu.cn>
Subject: Re: [PATCH] ceph: fix possible null-pointer dereference in
 ceph_mdsmap_decode()

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@...nghua.edu.cn>
> Signed-off-by: Tuo Li <islituo@...il.com>
> ---
>  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?

-- 
Jeff Layton <jlayton@...nel.org>