[PATCH] [lucid/master] nl80211: fix overflow in ssid_len - CVE-2011-2517

[Paolo Pisati]

When one of the SSID's length passed in a scan or sched_scan request
is larger than 255, there will be an overflow in the u8 that is used
to store the length before checking.  This causes the check to fail
and we overrun the buffer when copying the SSID.

Fix this by checking the nl80211 attribute length before copying it to
the struct.

This is a follow up for the previous commit
208c72f4fe44fe09577e7975ba0e7fa0278f3d03, which didn't fix the problem
entirely.

Reported-by: Ido Yariv <ido at wizery.com>
Signed-off-by: Luciano Coelho <coelho at ti.com>
Signed-off-by: John W. Linville <linville at tuxdriver.com>

CVE-2011-2517

BugLink: http://bugs.launchpad.net/bugs/869245

upstream commit 57a27e1d6a3bb9ad4efeebd3a8c71156d6207536

Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 net/wireless/nl80211.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index f0341e4..f72387f 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -2995,11 +2995,11 @@ static int nl80211_trigger_scan(struct sk_buff *skb, struct genl_info *info)
 	i = 0;
 	if (info->attrs[NL80211_ATTR_SCAN_SSIDS]) {
 		nla_for_each_nested(attr, info->attrs[NL80211_ATTR_SCAN_SSIDS], tmp) {
-			request->ssids[i].ssid_len = nla_len(attr);
-			if (request->ssids[i].ssid_len > IEEE80211_MAX_SSID_LEN) {
+			if (nla_len(attr) > IEEE80211_MAX_SSID_LEN) {
 				err = -EINVAL;
 				goto out_free;
 			}
+			request->ssids[i].ssid_len = nla_len(attr);
 			memcpy(request->ssids[i].ssid, nla_data(attr), nla_len(attr));
 			i++;
 		}
-- 
1.7.5.4