ipv6: fix ndisc_is_useropt() handling for PIO

The current logic only works if the PIO is between two
other ND user options.  This fixes it so that the PIO
can also be either before or after other ND user options
(for example the first or last option in the RA).

side note: there's actually Android tests verifying
a portion of the old broken behaviour, so:
  https://android-review.googlesource.com/c/kernel/tests/+/3196704
fixes those up.

Cc: Jen Linkova <[email protected]>
Cc: Lorenzo Colitti <[email protected]>
Cc: Patrick Rohr <[email protected]>
Cc: David Ahern <[email protected]>
Cc: YOSHIFUJI Hideaki / 吉藤英明 <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Signed-off-by: Maciej Żenczykowski <[email protected]>
Fixes: 048c796 ("ipv6: adjust ndisc_is_useropt() to also return true for PIO")
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: zenczykowski

net/ipv6/ndisc.c

@@ -227,6 +227,7 @@ struct ndisc_options *ndisc_parse_options(const struct net_device *dev,
 		return NULL;
 	memset(ndopts, 0, sizeof(*ndopts));
 	while (opt_len) {
+		bool unknown = false;
 		int l;
 		if (opt_len < sizeof(struct nd_opt_hdr))
 			return NULL;
@@ -262,22 +263,23 @@ struct ndisc_options *ndisc_parse_options(const struct net_device *dev,
 			break;
 #endif
 		default:
-			if (ndisc_is_useropt(dev, nd_opt)) {
-				ndopts->nd_useropts_end = nd_opt;
-				if (!ndopts->nd_useropts)
-					ndopts->nd_useropts = nd_opt;
-			} else {
-				/*
-				 * Unknown options must be silently ignored,
-				 * to accommodate future extension to the
-				 * protocol.
-				 */
-				ND_PRINTK(2, notice,
-					  "%s: ignored unsupported option; type=%d, len=%d\n",
-					  __func__,
-					  nd_opt->nd_opt_type,
-					  nd_opt->nd_opt_len);
-			}
+			unknown = true;
+		}
+		if (ndisc_is_useropt(dev, nd_opt)) {
+			ndopts->nd_useropts_end = nd_opt;
+			if (!ndopts->nd_useropts)
+				ndopts->nd_useropts = nd_opt;
+		} else if (unknown) {
+			/*
+			 * Unknown options must be silently ignored,
+			 * to accommodate future extension to the
+			 * protocol.
+			 */
+			ND_PRINTK(2, notice,
+				  "%s: ignored unsupported option; type=%d, len=%d\n",
+				  __func__,
+				  nd_opt->nd_opt_type,
+				  nd_opt->nd_opt_len);
 		}
 next_opt:
 		opt_len -= l;