[PATCH 4.9 77/97] cfg80211: fix page refcount issue in A-MSDU decap

[Greg Kroah-Hartman]

From: Felix Fietkau <nbd@xxxxxxxx>

commit 81c044fc3bdc5b7be967cd3682528ea94b58c06a upstream.

The fragments attached to a skb can be part of a compound page. In that case,
page_ref_inc will increment the refcount for the wrong page. Fix this by
using get_page instead, which calls page_ref_inc on the compound head and
also checks for overflow.

Fixes: 2b67f944f88c ("cfg80211: reuse existing page fragments in A-MSDU rx")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Felix Fietkau <nbd@xxxxxxxx>
Link: https://lore.kernel.org/r/20200113182107.20461-1-nbd@xxxxxxxx
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/wireless/util.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -653,7 +653,7 @@ __frame_add_frag(struct sk_buff *skb, st
 	struct skb_shared_info *sh = skb_shinfo(skb);
 	int page_offset;
 
-	page_ref_inc(page);
+	get_page(page);
 	page_offset = ptr - page_address(page);
 	skb_add_rx_frag(skb, sh->nr_frags, page, page_offset, len, size);
 }