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[73.241.150.70]) by smtp.gmail.com with ESMTPSA id 6sm32425457pfv.30.2019.01.22.18.51.45 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Jan 2019 18:51:45 -0800 (PST) Subject: Re: [PATCH net-next v1] l2tp: fix reading optional fields To: Jacob Wen , netdev@vger.kernel.org Cc: jchapman@katalix.com References: <20190123023050.29062-1-jian.w.wen@oracle.com> From: Eric Dumazet Message-ID: Date: Tue, 22 Jan 2019 18:51:45 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190123023050.29062-1-jian.w.wen@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 01/22/2019 06:30 PM, Jacob Wen wrote: > Use pskb_may_pull() to make sure the optional fields are in skb linear > parts. > > Signed-off-by: Jacob Wen > --- > v1: fix warning: ISO C90 forbids mixed declarations and code > --- > net/l2tp/l2tp_core.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c > index 26f1d435696a..c0dfa2bcd218 100644 > --- a/net/l2tp/l2tp_core.c > +++ b/net/l2tp/l2tp_core.c > @@ -627,6 +627,8 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, > > /* Parse and check optional cookie */ > if (session->peer_cookie_len > 0) { > + if (!pskb_may_pull(skb, ptr - optr + session->peer_cookie_len)) > + goto discard; This is completely buggy. After pskb_may_pull(), the ptr and optr pointers might point to freed data. So the memcmp() might crash hard. > if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) { > l2tp_info(tunnel, L2TP_MSG_DATA, > "%s: cookie mismatch (%u/%u). Discarding.\n", > @@ -649,6 +651,8 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, > L2TP_SKB_CB(skb)->has_seq = 0; > if (tunnel->version == L2TP_HDR_VER_2) { > if (hdrflags & L2TP_HDRFLAG_S) { > + if (!pskb_may_pull(skb, ptr - optr + 4)) > + goto discard; > ns = ntohs(*(__be16 *) ptr); > ptr += 2; > nr = ntohs(*(__be16 *) ptr); > @@ -663,8 +667,12 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, > session->name, ns, nr, session->nr); > } > } else if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) { > - u32 l2h = ntohl(*(__be32 *) ptr); > + u32 l2h; > + > + if (!pskb_may_pull(skb, ptr - optr + 4)) > + goto discard; > > + l2h = ntohl(*(__be32 *) ptr); > if (l2h & 0x40000000) { > ns = l2h & 0x00ffffff; > > @@ -729,6 +737,8 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, > if (tunnel->version == L2TP_HDR_VER_2) { > /* If offset bit set, skip it. */ > if (hdrflags & L2TP_HDRFLAG_O) { > + if (!pskb_may_pull(skb, ptr - optr + 2)) > + goto discard; > offset = ntohs(*(__be16 *)ptr); > ptr += 2 + offset; > } >