!12788 slip: make slhc_remember() more robust against malicious packets

Merge Pull Request from: @ci-robot 
 
PR sync from: Liu Jian <[email protected]>
https://mailweb.openeuler.org/hyperkitty/list/[email protected]/message/CRUCXO4XFI72W55SUYXV73DJGXF5OGFL/ 
 
https://gitee.com/src-openeuler/kernel/issues/IAYRFT 
 
Link:https://gitee.com/openeuler/kernel/pulls/12788 

Reviewed-by: Yue Haibing <[email protected]> 
Signed-off-by: Yang Yingliang <[email protected]>

drivers/net/slip/slhc.c

@@ -643,46 +643,57 @@ slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
 int
 slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
 {
-	struct cstate *cs;
-	unsigned ihl;
-
+	const struct tcphdr *th;
 	unsigned char index;
+	struct iphdr *iph;
+	struct cstate *cs;
+	unsigned int ihl;
 
-	if(isize < 20) {
-		/* The packet is shorter than a legal IP header */
+	/* The packet is shorter than a legal IP header.
+	 * Also make sure isize is positive.
+	 */
+	if (isize < (int)sizeof(struct iphdr)) {
+runt:
 		comp->sls_i_runt++;
-		return slhc_toss( comp );
+		return slhc_toss(comp);
 	}
+	iph = (struct iphdr *)icp;
 	/* Peek at the IP header's IHL field to find its length */
-	ihl = icp[0] & 0xf;
-	if(ihl < 20 / 4){
-		/* The IP header length field is too small */
-		comp->sls_i_runt++;
-		return slhc_toss( comp );
-	}
-	index = icp[9];
-	icp[9] = IPPROTO_TCP;
+	ihl = iph->ihl;
+	/* The IP header length field is too small,
+	 * or packet is shorter than the IP header followed
+	 * by minimal tcp header.
+	 */
+	if (ihl < 5 || isize < ihl * 4 + sizeof(struct tcphdr))
+		goto runt;
+
+	index = iph->protocol;
+	iph->protocol = IPPROTO_TCP;
 
 	if (ip_fast_csum(icp, ihl)) {
 		/* Bad IP header checksum; discard */
 		comp->sls_i_badcheck++;
-		return slhc_toss( comp );
+		return slhc_toss(comp);
 	}
-	if(index > comp->rslot_limit) {
+	if (index > comp->rslot_limit) {
 		comp->sls_i_error++;
 		return slhc_toss(comp);
 	}
-
+	th = (struct tcphdr *)(icp + ihl * 4);
+	if (th->doff < sizeof(struct tcphdr) / 4)
+		goto runt;
+	if (isize < ihl * 4 + th->doff * 4)
+		goto runt;
 	/* Update local state */
 	cs = &comp->rstate[comp->recv_current = index];
 	comp->flags &=~ SLF_TOSS;
-	memcpy(&cs->cs_ip,icp,20);
-	memcpy(&cs->cs_tcp,icp + ihl*4,20);
+	memcpy(&cs->cs_ip, iph, sizeof(*iph));
+	memcpy(&cs->cs_tcp, th, sizeof(*th));
 	if (ihl > 5)
-	  memcpy(cs->cs_ipopt, icp + sizeof(struct iphdr), (ihl - 5) * 4);
-	if (cs->cs_tcp.doff > 5)
-	  memcpy(cs->cs_tcpopt, icp + ihl*4 + sizeof(struct tcphdr), (cs->cs_tcp.doff - 5) * 4);
-	cs->cs_hsize = ihl*2 + cs->cs_tcp.doff*2;
+	  memcpy(cs->cs_ipopt, &iph[1], (ihl - 5) * 4);
+	if (th->doff > 5)
+	  memcpy(cs->cs_tcpopt, &th[1], (th->doff - 5) * 4);
+	cs->cs_hsize = ihl*2 + th->doff*2;
 	cs->initialized = true;
 	/* Put headers back on packet
 	 * Neither header checksum is recalculated