[PATCH] wifi: libipw: fix key index receive bound checks

[Pengpeng Hou]

libipw_rx() reads skb->data[hdrlen + 3] to extract the WEP key index in
both the software-decrypt key selection path and the hardware-decrypted
IV/ICV strip path. In both places the existing guard only checks
skb->len >= hdrlen + 3, which proves bytes up to hdrlen + 2 but not the
byte at hdrlen + 3.

Require hdrlen + 4 bytes before reading that item in both paths. This is
a local source-boundary check only; it does not change the key index
semantics.

Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
diff --git a/drivers/net/wireless/intel/ipw2x00/libipw_rx.c b/drivers/net/wireless/intel/ipw2x00/libipw_rx.c
--- a/drivers/net/wireless/intel/ipw2x00/libipw_rx.c
+++ b/drivers/net/wireless/intel/ipw2x00/libipw_rx.c
@@ -414,7 +414,7 @@
 	    ieee->host_mc_decrypt : ieee->host_decrypt;
 
 	if (can_be_decrypted) {
-		if (skb->len >= hdrlen + 3) {
+		if (skb->len >= hdrlen + 4) {
 			/* Top two-bits of byte 3 are the key index */
 			keyidx = skb->data[hdrlen + 3] >> 6;
 		}
@@ -660,7 +660,7 @@
 		int trimlen = 0;
 
 		/* Top two-bits of byte 3 are the key index */
-		if (skb->len >= hdrlen + 3)
+		if (skb->len >= hdrlen + 4)
 			keyidx = skb->data[hdrlen + 3] >> 6;
 
 		/* To strip off any security data which appears before the