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cfg80211: add and use strongly typed element iteration macros

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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>
This commit is contained in:
Johannes Berg 2019-02-07 21:44:41 +01:00
parent 341203e789
commit 0f3b07f027
2 changed files with 59 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
include/linux/ieee80211.h
View File

@ -3243,4 +3243,57 @@ static inline bool ieee80211_action_contains_tpc(struct sk_buff *skb)
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 */

14
net/wireless/scan.c
View File

@ -484,6 +484,8 @@ const u8 *cfg80211_find_ie_match(u8 eid, const u8 *ies, int len,
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, const u8 *ies, int len,
(!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;