Re: [bug report] net: ipv4: Move ip_options_fragment() out of loop

August 27, 2021 4:49 PM, "Dan Carpenter" [off-list ref] wrote:

Hello Yajun Deng,

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

Can you test the attached?

Thanks.

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