[PATCH v2] wifi: cfg80211: validate IEs in cfg80211_wext_siwgenie()

[Deepanshu Kartikey <kartikey406@gmail.com>]

The KASAN allocation trace shows that a malformed IE buffer is
stored via SIOCSIWGENIE (cfg80211_wext_siwgenie()) without any
validation. The crash trace shows that a subsequent SIOCSIWESSID
triggers a connection attempt which calls cfg80211_sme_get_conn_ies()
to process the stored IE buffer, causing:

 - An out-of-bounds read in skip_ie() which reads ies[pos+1]
   (the length byte) past the end of the 1-byte buffer.

 - An integer underflow in the memcpy size argument when offs
   returned by ieee80211_ie_split() exceeds ies_len, causing
   unsigned subtraction to wrap to SIZE_MAX and triggering a
   fortify panic.

Fix this by validating the IE buffer in cfg80211_wext_siwgenie()
before storing it. First reject buffers smaller than 2 bytes since
a valid IE requires at least a type and length field. Then use
for_each_element() and for_each_element_completed() to verify all
elements are well-formed. Return -EINVAL if validation fails.

Reported-by: syzbot+cc867e537e4bd36f69bb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=cc867e537e4bd36f69bb
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>

---
v2: Use for_each_element() and for_each_element_completed() instead
    of open-coded validation loop, as suggested by Johannes Berg.
    Also add explicit ie_len < 2 check to handle the case where
    for_each_element_completed() returns true for a 1-byte buffer.
---
 net/wireless/wext-sme.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/net/wireless/wext-sme.c b/net/wireless/wext-sme.c
index 573b6b15a446..51fc2617a1c3 100644
--- a/net/wireless/wext-sme.c
+++ b/net/wireless/wext-sme.c
@@ -319,6 +319,18 @@ int cfg80211_wext_siwgenie(struct net_device *dev,
 		return 0;
 
 	if (ie_len) {
+		const struct element *elem;
+
+		 /* IE must have at least Type + Length bytes */
+		if (ie_len < 2)
+			return -EINVAL;
+		for_each_element(elem, extra, ie_len) {
+			/* nothing */
+		}
+
+		if (!for_each_element_completed(elem, extra, ie_len))
+			return -EINVAL;
+
 		ie = kmemdup(extra, ie_len, GFP_KERNEL);
 		if (!ie)
 			return -ENOMEM;
-- 
2.43.0