net: ipv4: Move ip_options_fragment() out of loop

Hello Yajun Deng,

This is a semi-automatic email about new static checker warnings.

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)

net/ipv4/ip_output.c

   827			ip_fraglist_init(skb, iph, hlen, &iter);
                                                         ^^^^^

iter.frag is set here.

   828			ip_options_fragment(iter.frag);
                                            ^^^^^^^^^

The patch introduces a new dereference here

829
830 for (;;) {
831 /* Prepare header of the next frame,
832 * before previous one went down. */

   833				if (iter.frag) {
                                    ^^^^^^^^^

But the old code assumed that "iter.frag" could be NULL.

   834					IPCB(iter.frag)->flags = IPCB(skb)->flags;
   835					ip_fraglist_prepare(skb, &iter);

regards,
dan carpenter

Can you test the attached?

Thanks.

From 19fda71966403608c3b2dc981b238a1c25865b83 Mon Sep 17 00:00:00 2001
From: Yajun Deng <[email protected]>
Date: Fri, 27 Aug 2021 17:14:43 +0800
Subject: [PATCH net-next] net: ipv4: Fix the warning for dereference

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)

Add a if statements to avoid the warning.

---
 net/ipv4/ip_output.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index 9a8f05d5476e..9bca57ef8b83 100644
@@ -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

Looks good. Thanks!

regards,
dan carpenter