netdev - AW: [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

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Date:   Fri, 25 Jun 2021 10:06:26 +0000
From:   Walter Harms <wharms@....de>
To:     Colin King <colin.king@...onical.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        "Florian Westphal" <fw@...len.de>,
        "David S . Miller" <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "coreteam@...filter.org" <coreteam@...filter.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: AW: [PATCH][next] netfilter: nf_tables: Fix dereference of null
 pointer flow

hi Colin,
most free_something_functions accept NULL
these days, perhaps it would be more efficient
to add a check in nft_flow_rule_destroy().
There is a chance that this will catch the same
mistake in future  also.

jm2c,
re,
 wh
________________________________________
Von: Colin King <colin.king@...onical.com>
Gesendet: Donnerstag, 24. Juni 2021 21:57:18
An: Pablo Neira Ayuso; Jozsef Kadlecsik; Florian Westphal; David S . Miller; Jakub Kicinski; netfilter-devel@...r.kernel.org; coreteam@...filter.org; netdev@...r.kernel.org
Cc: kernel-janitors@...r.kernel.org; linux-kernel@...r.kernel.org
Betreff: [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

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From: Colin Ian King <colin.king@...onical.com>

In the case where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
nft_flow_rule_create is not called and flow is NULL. The subsequent
error handling execution via label err_destroy_flow_rule will lead
to a null pointer dereference on flow when calling nft_flow_rule_destroy.
Since the error path to err_destroy_flow_rule has to cater for null
and non-null flows, only call nft_flow_rule_destroy if flow is non-null
to fix this issue.

Addresses-Coverity: ("Explicity null dereference")
Fixes: 3c5e44622011 ("netfilter: nf_tables: memleak in hw offload abort path")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 net/netfilter/nf_tables_api.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 390d4466567f..de182d1f7c4e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3446,7 +3446,8 @@ static int nf_tables_newrule(struct sk_buff *skb, const struct nfnl_info *info,
        return 0;

 err_destroy_flow_rule:
-       nft_flow_rule_destroy(flow);
+       if (flow)
+               nft_flow_rule_destroy(flow);
 err_release_rule:
        nf_tables_rule_release(&ctx, rule);
 err_release_expr:
--
2.31.1