wifi: mac80211: fix slab-out-of-bounds read in ieee80211_monitor_select_queue()

ieee80211_monitor_select_queue() validates the skb length using skb->len
before dereferencing pointers into skb->data to access the 802.11 header.
However, skb->len includes data in both the linear head buffer and
non-linear fragments/pages. When AF_PACKET sends a packet large enough to
become non-linear, the 802.11 header at skb->data + len_rthdr may extend
past the linear head buffer even though skb->len appears sufficient.

This leads to a slab-out-of-bounds read when accessing hdr->frame_control,
as the kernel reads beyond the allocated skb head buffer:

  BUG: KASAN: slab-out-of-bounds in ieee80211_monitor_select_queue+0x1ed/0x220

syzbot has hit the same issues.

Fix this by checking skb_headlen(skb) (which gives the length of the
linear data region) instead of skb->len before dereferencing skb->data
pointers. This ensures the required bytes are actually present in the
linear portion of the skb.

Apply the same fix to ieee80211_validate_radiotap_len() which has the
same class of bug: it uses skb->len to validate accesses to skb->data,
and to the corresponding checks in ieee80211_monitor_start_xmit(): for
drivers advertising NETIF_F_SG the skb is not linearized before
ndo_start_xmit, so the 802.11 header can be read past the linear
buffer there as well.

Fixes: cf0277e714 ("mac80211: fix skb buffering issue")
Fixes: 9b8a74e348 ("[MAC80211]: Improve sanity checks on injected packets")
Reported-by: [email protected]
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=610e40369bc02181bad0
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=878643e0580bc580f883
Assisted-by: GitHub-Copilot:claude-opus-4.6
Signed-off-by: Cen Zhang (Microsoft) <[email protected]>
Reviewed-by: Francis Perron <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Johannes Berg <[email protected]>

net/mac80211/iface.c

@@ -998,8 +998,8 @@ static u16 ieee80211_monitor_select_queue(struct net_device *dev,
 
 	len_rthdr = ieee80211_get_radiotap_len(skb->data);
 	hdr = (struct ieee80211_hdr *)(skb->data + len_rthdr);
-	if (skb->len < len_rthdr + 2 ||
-	    skb->len < len_rthdr + ieee80211_hdrlen(hdr->frame_control))
+	if (skb_headlen(skb) < len_rthdr + 2 ||
+	    skb_headlen(skb) < len_rthdr + ieee80211_hdrlen(hdr->frame_control))
 		return 0; /* doesn't matter, frame will be dropped */
 
 	return ieee80211_select_queue_80211(sdata, skb, hdr);

net/mac80211/tx.c

@@ -2091,7 +2091,7 @@ static bool ieee80211_validate_radiotap_len(struct sk_buff *skb)
 		(struct ieee80211_radiotap_header *)skb->data;
 
 	/* check for not even having the fixed radiotap header part */
-	if (unlikely(skb->len < sizeof(struct ieee80211_radiotap_header)))
+	if (unlikely(skb_headlen(skb) < sizeof(struct ieee80211_radiotap_header)))
 		return false; /* too short to be possibly valid */
 
 	/* is it a header version we can trust to find length from? */
@@ -2099,7 +2099,7 @@ static bool ieee80211_validate_radiotap_len(struct sk_buff *skb)
 		return false; /* only version 0 is supported */
 
 	/* does the skb contain enough to deliver on the alleged length? */
-	if (unlikely(skb->len < ieee80211_get_radiotap_len(skb->data)))
+	if (unlikely(skb_headlen(skb) < ieee80211_get_radiotap_len(skb->data)))
 		return false; /* skb too short for claimed rt header extent */
 
 	return true;
@@ -2388,13 +2388,13 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 	skb_set_network_header(skb, len_rthdr);
 	skb_set_transport_header(skb, len_rthdr);
 
-	if (skb->len < len_rthdr + 2)
+	if (skb_headlen(skb) < len_rthdr + 2)
 		goto fail;
 
 	hdr = (struct ieee80211_hdr *)(skb->data + len_rthdr);
 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
 
-	if (skb->len < len_rthdr + hdrlen)
+	if (skb_headlen(skb) < len_rthdr + hdrlen)
 		goto fail;
 
 	/*
@@ -2402,7 +2402,7 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 	 * carrying a rfc1042 header
 	 */
 	if (ieee80211_is_data(hdr->frame_control) &&
-	    skb->len >= len_rthdr + hdrlen + sizeof(rfc1042_header) + 2) {
+	    skb_headlen(skb) >= len_rthdr + hdrlen + sizeof(rfc1042_header) + 2) {
 		u8 *payload = (u8 *)hdr + hdrlen;
 
 		if (ether_addr_equal(payload, rfc1042_header))