wifi: cfg80211: rewrite merging of inherited elements

The cfg80211_gen_new_ie function merges the IEs using inheritance rules.
Rewrite this function to fix issues around inheritance rules. In
particular, vendor elements do not require any special handling, as they
are either all inherited or overridden by the subprofile.
Also, add fragmentation handling as this may be needed in some cases.

This also changes the function to not require making a copy. The new
version could be optimized a bit by explicitly tracking which IEs have
been handled already rather than looking that up again every time.

Note that a small behavioural change is the removal of the SSID special
handling. This should be fine for the MBSSID element, as the SSID must
be included in the subelement.

Fixes: 0b8fb823 ("cfg80211: Parsing of Multiple BSSID information in scanning")
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230616094949.bc6152e146db.I2b5f3bc45085e1901e5b5192a674436adaf94748@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/scan.c

@@ -259,117 +259,152 @@ bool cfg80211_is_element_inherited(const struct element *elem,
 }
 EXPORT_SYMBOL(cfg80211_is_element_inherited);
 
-static size_t cfg80211_gen_new_ie(const u8 *ie, size_t ielen,
-				  const u8 *subelement, size_t subie_len,
-				  u8 *new_ie, gfp_t gfp)
+static size_t cfg80211_copy_elem_with_frags(const struct element *elem,
+					    const u8 *ie, size_t ie_len,
+					    u8 **pos, u8 *buf, size_t buf_len)
 {
-	u8 *pos, *tmp;
-	const u8 *tmp_old, *tmp_new;
-	const struct element *non_inherit_elem;
-	u8 *sub_copy;
+	if (WARN_ON((u8 *)elem < ie || elem->data > ie + ie_len ||
+		    elem->data + elem->datalen > ie + ie_len))
+		return 0;
 
-	/* copy subelement as we need to change its content to
-	 * mark an ie after it is processed.
-	 */
-	sub_copy = kmemdup(subelement, subie_len, gfp);
-	if (!sub_copy)
+	if (elem->datalen + 2 > buf + buf_len - *pos)
+		return 0;
+
+	memcpy(*pos, elem, elem->datalen + 2);
+	*pos += elem->datalen + 2;
+
+	/* Finish if it is not fragmented  */
+	if (elem->datalen != 255)
+		return *pos - buf;
+
+	ie_len = ie + ie_len - elem->data - elem->datalen;
+	ie = (const u8 *)elem->data + elem->datalen;
+
+	for_each_element(elem, ie, ie_len) {
+		if (elem->id != WLAN_EID_FRAGMENT)
+			break;
+
+		if (elem->datalen + 2 > buf + buf_len - *pos)
 			return 0;
 
-	pos = &new_ie[0];
+		memcpy(*pos, elem, elem->datalen + 2);
+		*pos += elem->datalen + 2;
 
-	/* set new ssid */
-	tmp_new = cfg80211_find_ie(WLAN_EID_SSID, sub_copy, subie_len);
-	if (tmp_new) {
-		memcpy(pos, tmp_new, tmp_new[1] + 2);
-		pos += (tmp_new[1] + 2);
+		if (elem->datalen != 255)
+			break;
 	}
 
-	/* get non inheritance list if exists */
-	non_inherit_elem =
-		cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
-				       sub_copy, subie_len);
+	return *pos - buf;
+}
 
-	/* go through IEs in ie (skip SSID) and subelement,
-	 * merge them into new_ie
+static size_t cfg80211_gen_new_ie(const u8 *ie, size_t ielen,
+				  const u8 *subie, size_t subie_len,
+				  u8 *new_ie, size_t new_ie_len)
+{
+	const struct element *non_inherit_elem, *parent, *sub;
+	u8 *pos = new_ie;
+	u8 id, ext_id;
+	unsigned int match_len;
+
+	non_inherit_elem = cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
+						  subie, subie_len);
+
+	/* We copy the elements one by one from the parent to the generated
+	 * elements.
+	 * If they are not inherited (included in subie or in the non
+	 * inheritance element), then we copy all occurrences the first time
+	 * we see this element type.
 	 */
-	tmp_old = cfg80211_find_ie(WLAN_EID_SSID, ie, ielen);
-	tmp_old = (tmp_old) ? tmp_old + tmp_old[1] + 2 : ie;
+	for_each_element(parent, ie, ielen) {
+		if (parent->id == WLAN_EID_FRAGMENT)
+			continue;
 
-	while (tmp_old + 2 - ie <= ielen &&
-	       tmp_old + tmp_old[1] + 2 - ie <= ielen) {
-		if (tmp_old[0] == 0) {
-			tmp_old++;
+		if (parent->id == WLAN_EID_EXTENSION) {
+			if (parent->datalen < 1)
 				continue;
+
+			id = WLAN_EID_EXTENSION;
+			ext_id = parent->data[0];
+			match_len = 1;
+		} else {
+			id = parent->id;
+			match_len = 0;
 		}
 
-		if (tmp_old[0] == WLAN_EID_EXTENSION)
-			tmp = (u8 *)cfg80211_find_ext_ie(tmp_old[2], sub_copy,
-							 subie_len);
-		else
-			tmp = (u8 *)cfg80211_find_ie(tmp_old[0], sub_copy,
-						     subie_len);
+		/* Find first occurrence in subie */
+		sub = cfg80211_find_elem_match(id, subie, subie_len,
+					       &ext_id, match_len, 0);
 
-		if (!tmp) {
-			const struct element *old_elem = (void *)tmp_old;
+		/* Copy from parent if not in subie and inherited */
+		if (!sub &&
+		    cfg80211_is_element_inherited(parent, non_inherit_elem)) {
+			if (!cfg80211_copy_elem_with_frags(parent,
+							   ie, ielen,
+							   &pos, new_ie,
+							   new_ie_len))
+				return 0;
 
-			/* ie in old ie but not in subelement */
-			if (cfg80211_is_element_inherited(old_elem,
-							  non_inherit_elem)) {
-				memcpy(pos, tmp_old, tmp_old[1] + 2);
-				pos += tmp_old[1] + 2;
-			}
-		} else {
-			/* ie in transmitting ie also in subelement,
-			 * copy from subelement and flag the ie in subelement
-			 * as copied (by setting eid field to WLAN_EID_SSID,
-			 * which is skipped anyway).
-			 * For vendor ie, compare OUI + type + subType to
-			 * determine if they are the same ie.
-			 */
-			if (tmp_old[0] == WLAN_EID_VENDOR_SPECIFIC) {
-				if (tmp_old[1] >= 5 && tmp[1] >= 5 &&
-				    !memcmp(tmp_old + 2, tmp + 2, 5)) {
-					/* same vendor ie, copy from
-					 * subelement
-					 */
-					memcpy(pos, tmp, tmp[1] + 2);
-					pos += tmp[1] + 2;
-					tmp[0] = WLAN_EID_SSID;
-				} else {
-					memcpy(pos, tmp_old, tmp_old[1] + 2);
-					pos += tmp_old[1] + 2;
+			continue;
 		}
-			} else {
-				/* copy ie from subelement into new ie */
-				memcpy(pos, tmp, tmp[1] + 2);
-				pos += tmp[1] + 2;
-				tmp[0] = WLAN_EID_SSID;
+
+		/* Already copied if an earlier element had the same type */
+		if (cfg80211_find_elem_match(id, ie, (u8 *)parent - ie,
+					     &ext_id, match_len, 0))
+			continue;
+
+		/* Not inheriting, copy all similar elements from subie */
+		while (sub) {
+			if (!cfg80211_copy_elem_with_frags(sub,
+							   subie, subie_len,
+							   &pos, new_ie,
+							   new_ie_len))
+				return 0;
+
+			sub = cfg80211_find_elem_match(id,
+						       sub->data + sub->datalen,
+						       subie_len + subie -
+						       (sub->data +
+							sub->datalen),
+						       &ext_id, match_len, 0);
 		}
 	}
 
-		if (tmp_old + tmp_old[1] + 2 - ie == ielen)
-			break;
+	/* The above misses elements that are included in subie but not in the
+	 * parent, so do a pass over subie and append those.
+	 * Skip the non-tx BSSID caps and non-inheritance element.
+	 */
+	for_each_element(sub, subie, subie_len) {
+		if (sub->id == WLAN_EID_NON_TX_BSSID_CAP)
+			continue;
+
+		if (sub->id == WLAN_EID_FRAGMENT)
+			continue;
 
-		tmp_old += tmp_old[1] + 2;
+		if (sub->id == WLAN_EID_EXTENSION) {
+			if (sub->datalen < 1)
+				continue;
+
+			id = WLAN_EID_EXTENSION;
+			ext_id = sub->data[0];
+			match_len = 1;
+
+			if (ext_id == WLAN_EID_EXT_NON_INHERITANCE)
+				continue;
+		} else {
+			id = sub->id;
+			match_len = 0;
 		}
 
-	/* go through subelement again to check if there is any ie not
-	 * copied to new ie, skip ssid, capability, bssid-index ie
-	 */
-	tmp_new = sub_copy;
-	while (tmp_new + 2 - sub_copy <= subie_len &&
-	       tmp_new + tmp_new[1] + 2 - sub_copy <= subie_len) {
-		if (!(tmp_new[0] == WLAN_EID_NON_TX_BSSID_CAP ||
-		      tmp_new[0] == WLAN_EID_SSID)) {
-			memcpy(pos, tmp_new, tmp_new[1] + 2);
-			pos += tmp_new[1] + 2;
-		}
-		if (tmp_new + tmp_new[1] + 2 - sub_copy == subie_len)
-			break;
-		tmp_new += tmp_new[1] + 2;
+		/* Processed if one was included in the parent */
+		if (cfg80211_find_elem_match(id, ie, ielen,
+					     &ext_id, match_len, 0))
+			continue;
+
+		if (!cfg80211_copy_elem_with_frags(sub, subie, subie_len,
+						   &pos, new_ie, new_ie_len))
+			return 0;
 	}
 
-	kfree(sub_copy);
 	return pos - new_ie;
 }
 
@@ -2228,7 +2263,7 @@ static void cfg80211_parse_mbssid_data(struct wiphy *wiphy,
 			new_ie_len = cfg80211_gen_new_ie(ie, ielen,
 							 profile,
 							 profile_len, new_ie,
-							 gfp);
+							 IEEE80211_MAX_DATA_LEN);
 			if (!new_ie_len)
 				continue;