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Subject[PATCH 4.19 112/114] cfg80211: add and use strongly typed element iteration macros
Date
From: Johannes Berg <johannes.berg@intel.com>

commit 0f3b07f027f87a38ebe5c436490095df762819be upstream.

Rather than always iterating elements from frames with pure
u8 pointers, add a type "struct element" that encapsulates
the id/datalen/data format of them.

Then, add the element iteration macros
* for_each_element
* for_each_element_id
* for_each_element_extid

which take, as their first 'argument', such a structure and
iterate through a given u8 array interpreting it as elements.

While at it and since we'll need it, also add
* for_each_subelement
* for_each_subelement_id
* for_each_subelement_extid

which instead of taking data/length just take an outer element
and use its data/datalen.

Also add for_each_element_completed() to determine if any of
the loops above completed, i.e. it was able to parse all of
the elements successfully and no data remained.

Use for_each_element_id() in cfg80211_find_ie_match() as the
first user of this.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/ieee80211.h | 53 ++++++++++++++++++++++++++++++++++++++++++++++
net/wireless/scan.c | 14 +++++-------
2 files changed, 59 insertions(+), 8 deletions(-)

--- a/include/linux/ieee80211.h
+++ b/include/linux/ieee80211.h
@@ -3185,4 +3185,57 @@ static inline bool ieee80211_action_cont
return true;
}

+struct element {
+ u8 id;
+ u8 datalen;
+ u8 data[];
+};
+
+/* element iteration helpers */
+#define for_each_element(element, _data, _datalen) \
+ for (element = (void *)(_data); \
+ (u8 *)(_data) + (_datalen) - (u8 *)element >= \
+ sizeof(*element) && \
+ (u8 *)(_data) + (_datalen) - (u8 *)element >= \
+ sizeof(*element) + element->datalen; \
+ element = (void *)(element->data + element->datalen))
+
+#define for_each_element_id(element, _id, data, datalen) \
+ for_each_element(element, data, datalen) \
+ if (element->id == (_id))
+
+#define for_each_element_extid(element, extid, data, datalen) \
+ for_each_element(element, data, datalen) \
+ if (element->id == WLAN_EID_EXTENSION && \
+ element->datalen > 0 && \
+ element->data[0] == (extid))
+
+#define for_each_subelement(sub, element) \
+ for_each_element(sub, (element)->data, (element)->datalen)
+
+#define for_each_subelement_id(sub, id, element) \
+ for_each_element_id(sub, id, (element)->data, (element)->datalen)
+
+#define for_each_subelement_extid(sub, extid, element) \
+ for_each_element_extid(sub, extid, (element)->data, (element)->datalen)
+
+/**
+ * for_each_element_completed - determine if element parsing consumed all data
+ * @element: element pointer after for_each_element() or friends
+ * @data: same data pointer as passed to for_each_element() or friends
+ * @datalen: same data length as passed to for_each_element() or friends
+ *
+ * This function returns %true if all the data was parsed or considered
+ * while walking the elements. Only use this if your for_each_element()
+ * loop cannot be broken out of, otherwise it always returns %false.
+ *
+ * If some data was malformed, this returns %false since the last parsed
+ * element will not fill the whole remaining data.
+ */
+static inline bool for_each_element_completed(const struct element *element,
+ const void *data, size_t datalen)
+{
+ return (u8 *)element == (u8 *)data + datalen;
+}
+
#endif /* LINUX_IEEE80211_H */
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -484,6 +484,8 @@ const u8 *cfg80211_find_ie_match(u8 eid,
const u8 *match, int match_len,
int match_offset)
{
+ const struct element *elem;
+
/* match_offset can't be smaller than 2, unless match_len is
* zero, in which case match_offset must be zero as well.
*/
@@ -491,14 +493,10 @@ const u8 *cfg80211_find_ie_match(u8 eid,
(!match_len && match_offset)))
return NULL;

- while (len >= 2 && len >= ies[1] + 2) {
- if ((ies[0] == eid) &&
- (ies[1] + 2 >= match_offset + match_len) &&
- !memcmp(ies + match_offset, match, match_len))
- return ies;
-
- len -= ies[1] + 2;
- ies += ies[1] + 2;
+ for_each_element_id(elem, eid, ies, len) {
+ if (elem->datalen >= match_offset - 2 + match_len &&
+ !memcmp(elem->data + match_offset - 2, match, match_len))
+ return (void *)elem;
}

return NULL;

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