[PATCH] brcmfmac: avoid writing channel out of allocated array

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

Our code was assigning number of channels to the index variable by
default. If firmware reported channel we didn't predict this would
result in using that initial index value and writing out of array.

Fix this by detecting unexpected channel and ignoring it.

Fixes: 58de92d2f95e ("brcmfmac: use static superset of channels for wiphy bands")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
I'm not sure what kind of material it is. It fixes possible memory corruption
(serious thing?) but this bug was there since Apr 2015, so is it worth fixing
in 4.10? Or maybe I should even cc stable?
I don't think any released firmware reports any unexpected channel, so I guess
noone ever hit this problem. I just noticed this possible problem when working
on another feature.
---
 .../broadcom/brcm80211/brcmfmac/cfg80211.c         | 29 +++++++++++-----------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
index 13ca3eb..0babfc7 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
@@ -5825,7 +5825,6 @@ static int brcmf_construct_chaninfo(struct brcmf_cfg80211_info *cfg,
 	u32 i, j;
 	u32 total;
 	u32 chaninfo;
-	u32 index;
 
 	pbuf = kzalloc(BRCMF_DCMD_MEDLEN, GFP_KERNEL);
 
@@ -5873,33 +5872,33 @@ static int brcmf_construct_chaninfo(struct brcmf_cfg80211_info *cfg,
 		    ch.bw == BRCMU_CHAN_BW_80)
 			continue;
 
-		channel = band->channels;
-		index = band->n_channels;
+		channel = NULL;
 		for (j = 0; j < band->n_channels; j++) {
-			if (channel[j].hw_value == ch.control_ch_num) {
-				index = j;
+			if (band->channels[j].hw_value == ch.control_ch_num) {
+				channel = &band->channels[j];
 				break;
 			}
 		}
-		channel[index].center_freq =
-			ieee80211_channel_to_frequency(ch.control_ch_num,
-						       band->band);
-		channel[index].hw_value = ch.control_ch_num;
+		if (!channel) {
+			brcmf_err("Firmware reported unexpected channel %d\n",
+				  ch.control_ch_num);
+			continue;
+		}
 
 		/* assuming the chanspecs order is HT20,
 		 * HT40 upper, HT40 lower, and VHT80.
 		 */
 		if (ch.bw == BRCMU_CHAN_BW_80) {
-			channel[index].flags &= ~IEEE80211_CHAN_NO_80MHZ;
+			channel->flags &= ~IEEE80211_CHAN_NO_80MHZ;
 		} else if (ch.bw == BRCMU_CHAN_BW_40) {
-			brcmf_update_bw40_channel_flag(&channel[index], &ch);
+			brcmf_update_bw40_channel_flag(channel, &ch);
 		} else {
 			/* enable the channel and disable other bandwidths
 			 * for now as mentioned order assure they are enabled
 			 * for subsequent chanspecs.
 			 */
-			channel[index].flags = IEEE80211_CHAN_NO_HT40 |
-					       IEEE80211_CHAN_NO_80MHZ;
+			channel->flags = IEEE80211_CHAN_NO_HT40 |
+					 IEEE80211_CHAN_NO_80MHZ;
 			ch.bw = BRCMU_CHAN_BW_20;
 			cfg->d11inf.encchspec(&ch);
 			chaninfo = ch.chspec;
@@ -5907,11 +5906,11 @@ static int brcmf_construct_chaninfo(struct brcmf_cfg80211_info *cfg,
 						       &chaninfo);
 			if (!err) {
 				if (chaninfo & WL_CHAN_RADAR)
-					channel[index].flags |=
+					channel->flags |=
 						(IEEE80211_CHAN_RADAR |
 						 IEEE80211_CHAN_NO_IR);
 				if (chaninfo & WL_CHAN_PASSIVE)
-					channel[index].flags |=
+					channel->flags |=
 						IEEE80211_CHAN_NO_IR;
 			}
 		}
-- 
2.10.1