Commit 83f5e2cf authored by Johannes Berg's avatar Johannes Berg Committed by John W. Linville
Browse files

cfg80211: prohibit scanning the same channel more than once

It isn't very useful to scan the same channel more than once
during a given scan, and some hardware (notably iwlwifi) can
only scan a limited number of channels at a time. To prevent
any overflows, simply disallow scanning any channel multiple
times in a given scan command. This is a small change in the
userspace ABI, but the only user, wpa_supplicant, never asks
for a scan with the same frequency listed twice.
Signed-off-by: default avatarJohannes Berg <>
Signed-off-by: default avatarJohn W. Linville <>
parent 386aa23d
......@@ -2695,6 +2695,31 @@ static int nl80211_set_reg(struct sk_buff *skb, struct genl_info *info)
return r;
static int validate_scan_freqs(struct nlattr *freqs)
struct nlattr *attr1, *attr2;
int n_channels = 0, tmp1, tmp2;
nla_for_each_nested(attr1, freqs, tmp1) {
* Some hardware has a limited channel list for
* scanning, and it is pretty much nonsensical
* to scan for a channel twice, so disallow that
* and don't require drivers to check that the
* channel list they get isn't longer than what
* they can scan, as long as they can scan all
* the channels they registered at once.
nla_for_each_nested(attr2, freqs, tmp2)
if (attr1 != attr2 &&
nla_get_u32(attr1) == nla_get_u32(attr2))
return 0;
return n_channels;
static int nl80211_trigger_scan(struct sk_buff *skb, struct genl_info *info)
struct cfg80211_registered_device *drv;
......@@ -2704,7 +2729,7 @@ static int nl80211_trigger_scan(struct sk_buff *skb, struct genl_info *info)
struct ieee80211_channel *channel;
struct nlattr *attr;
struct wiphy *wiphy;
int err, tmp, n_ssids = 0, n_channels = 0, i;
int err, tmp, n_ssids = 0, n_channels, i;
enum ieee80211_band band;
size_t ie_len;
......@@ -2735,13 +2760,15 @@ static int nl80211_trigger_scan(struct sk_buff *skb, struct genl_info *info)
if (info->attrs[NL80211_ATTR_SCAN_FREQUENCIES]) {
nla_for_each_nested(attr, info->attrs[NL80211_ATTR_SCAN_FREQUENCIES], tmp)
n_channels = validate_scan_freqs(
if (!n_channels) {
err = -EINVAL;
goto out;
} else {
n_channels = 0;
for (band = 0; band < IEEE80211_NUM_BANDS; band++)
if (wiphy->bands[band])
n_channels += wiphy->bands[band]->n_channels;
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