linux-kernel - [PATCH net-next] net: ipv4: Fix the warning for dereference

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Message-Id: <20210830091640.14739-1-yajun.deng@linux.dev>
Date:   Mon, 30 Aug 2021 17:16:40 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yajun Deng <yajun.deng@...ux.dev>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: [PATCH net-next] net: ipv4: Fix the warning for dereference

Add a if statements to avoid the warning.

Dan Carpenter report:
The patch faf482ca196a: "net: ipv4: Move ip_options_fragment() out of
loop" from Aug 23, 2021, leads to the following Smatch complaint:

    net/ipv4/ip_output.c:833 ip_do_fragment()
    warn: variable dereferenced before check 'iter.frag' (see line 828)

Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Fixes: faf482ca196a ("net: ipv4: Move ip_options_fragment() out of loop")
Link: https://lore.kernel.org/netdev/20210830073802.GR7722@kadam/T/#t
Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
---
 net/ipv4/ip_output.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9a8f05d5476e..9bca57ef8b83 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -825,7 +825,9 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 
 		/* Everything is OK. Generate! */
 		ip_fraglist_init(skb, iph, hlen, &iter);
-		ip_options_fragment(iter.frag);
+
+		if (iter.frag)
+			ip_options_fragment(iter.frag);
 
 		for (;;) {
 			/* Prepare header of the next frame,
-- 
2.32.0