linux-kernel - Re: [PATCH] net/ipv4: fix potential NULL dereference in sisfb_post

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Date:   Fri, 1 Apr 2022 10:09:26 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Haowen Bai <baihaowen@...zu.com>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/ipv4: fix potential NULL dereference in
 sisfb_post_sis300()


On 3/31/22 20:57, Haowen Bai wrote:
> psin and psl could be null without checking null and return, so
> we need to dereference after checking.
>
> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
> ---
>   net/ipv4/igmp.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index 2ad3c7b..d400080 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -2569,7 +2569,7 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
>   	    copy_to_user(optval, msf, IP_MSFILTER_SIZE(0))) {
>   		return -EFAULT;
>   	}
> -	if (len &&
> +	if (len && psl &&


len can not be !0 here if len was 0

psl = rtnl_dereference(pmc->sflist);

if (!psl) {

    count = 0;


->len == 0


>   	    copy_to_user(&optval->imsf_slist_flex[0], psl->sl_addr, len))
>   		return -EFAULT;
>   	return 0;
> @@ -2608,7 +2608,7 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
>   	count = psl ? psl->sl_count : 0;
>   	copycount = count < gsf->gf_numsrc ? count : gsf->gf_numsrc;
>   	gsf->gf_numsrc = count;
> -	for (i = 0; i < copycount; i++, p++) {
> +	for (i = 0; i < copycount && psin && psl; i++, p++) {
>   		struct sockaddr_storage ss;
>   
>   		psin = (struct sockaddr_in *)&ss;


Same here.