Thread (152 messages) 152 messages, 21 authors, 2021-08-13

Re: [PATCH 02/64] mac80211: Use flex-array for radiotap header bitmap

From: David Sterba <hidden>
Date: 2021-07-28 09:26:14
Also in: dri-devel, linux-block, linux-hardening, linux-kbuild, linux-wireless, lkml, netdev

On Wed, Jul 28, 2021 at 10:35:56AM +0300, Dan Carpenter wrote:
quoted hunk ↗ jump to hunk
@@ -372,7 +372,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 			ieee80211_calculate_rx_timestamp(local, status,
 							 mpdulen, 0),
 			pos);
-		rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_TSFT);
+		rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_TSFT);
A drive-by comment, not related to the patchset, but rather the
ieee80211 driver itself.

Shift expressions with (1 << NUMBER) can be subtly broken once the
NUMBER is 31 and the value gets silently cast to a 64bit type. It will
become 0xfffffffff80000000.

I've checked the IEEE80211_RADIOTAP_* defintions if this is even remotely
possible and yes, IEEE80211_RADIOTAP_EXT == 31. Fortunatelly it seems to
be used with used with a 32bit types (eg. _bitmap_shifter) so there are
no surprises.

The recommended practice is to always use unsigned types for shifts, so
"1U << ..." at least.
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help