[PATCH 4.9 026/102] cfg80211: Fix array-bounds warning in fragment copy

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Kaehlcke <mka@xxxxxxxxxxxx>

commit aa1702dd162f420bf85ecef0c77686ef0dbc1496 upstream.

__ieee80211_amsdu_copy_frag intentionally initializes a pointer to
array[-1] to increment it later to valid values. clang rightfully
generates an array-bounds warning on the initialization statement.

Initialize the pointer to array[0] and change the algorithm from
increment before to increment after consume.

Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Cc: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/wireless/util.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -663,7 +663,7 @@ __ieee80211_amsdu_copy_frag(struct sk_bu
 			    int offset, int len)
 {
 	struct skb_shared_info *sh = skb_shinfo(skb);
-	const skb_frag_t *frag = &sh->frags[-1];
+	const skb_frag_t *frag = &sh->frags[0];
 	struct page *frag_page;
 	void *frag_ptr;
 	int frag_len, frag_size;
@@ -676,10 +676,10 @@ __ieee80211_amsdu_copy_frag(struct sk_bu
 
 	while (offset >= frag_size) {
 		offset -= frag_size;
-		frag++;
 		frag_page = skb_frag_page(frag);
 		frag_ptr = skb_frag_address(frag);
 		frag_size = skb_frag_size(frag);
+		frag++;
 	}
 
 	frag_ptr += offset;
@@ -691,12 +691,12 @@ __ieee80211_amsdu_copy_frag(struct sk_bu
 	len -= cur_len;
 
 	while (len > 0) {
-		frag++;
 		frag_len = skb_frag_size(frag);
 		cur_len = min(len, frag_len);
 		__frame_add_frag(frame, skb_frag_page(frag),
 				 skb_frag_address(frag), cur_len, frag_len);
 		len -= cur_len;
+		frag++;
 	}
 }