Subject: Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8

From: Florian Westphal <[email-masked]>
Date: Sun, 2 Apr 2017 13:45:45 +0200

Eric Dumazet <[email-masked]> wrote:
> -	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
> +	for (i = sizeof(struct tcphdr); i < tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
>  		if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
>  			u_int16_t oldmss;

maybe I am low on caffeeine but this looks fine, for tcp header with
only tcpmss this boils down to "20 <= 24 - 4" so we acccess offsets 20-23 which seems ok.