wifi: radiotap: reject radiotap with unknown bits

The radiotap parser is currently only used with the radiotap
namespace (not with vendor namespaces), but if the undefined
field 18 is used, the alignment/size is unknown as well. In
this case, iterator->_next_ns_data isn't initialized (it's
only set for skipping vendor namespaces), and syzbot points
out that we later compare against this uninitialized value.

Fix this by moving the rejection of unknown radiotap fields
down to after the in-namespace lookup, so it will really use
iterator->_next_ns_data only for vendor namespaces, even in
case undefined fields are present.

Cc: stable@vger.kernel.org
Fixes: 33e5a2f ("wireless: update radiotap parser")
Reported-by: syzbot+b09c1af8764c0097bb19@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/69944a91.a70a0220.2c38d7.00fc.GAE@google.com
Link: https://patch.msgid.link/20260217120526.162647-2-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: jmberg-intel

net/wireless/radiotap.c

@@ -239,14 +239,14 @@ int ieee80211_radiotap_iterator_next(
 		default:
 			if (!iterator->current_namespace ||
 			    iterator->_arg_index >= iterator->current_namespace->n_bits) {
-				if (iterator->current_namespace == &radiotap_ns)
-					return -ENOENT;
 				align = 0;
 			} else {
 				align = iterator->current_namespace->align_size[iterator->_arg_index].align;
 				size = iterator->current_namespace->align_size[iterator->_arg_index].size;
 			}
 			if (!align) {
+				if (iterator->current_namespace == &radiotap_ns)
+					return -ENOENT;
 				/* skip all subsequent data */
 				iterator->_arg = iterator->_next_ns_data;
 				/* give up on this namespace */