[PATCH AUTOSEL 4.14 2/2] wifi: brcmfmac: Fix field-spanning write in brcmf_scan_params_v2_to_v1()

[Sasha Levin]

From: Hans de Goede <hdegoede@xxxxxxxxxx>

[ Upstream commit 16e455a465fca91907af0108f3d013150386df30 ]

Using brcmfmac with 6.5-rc3 on a brcmfmac43241b4-sdio triggers
a backtrace caused by the following field-spanning warning:

memcpy: detected field-spanning write (size 120) of single field
  "&params_le->channel_list[0]" at
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:1072 (size 2)

The driver still works after this warning. The warning was introduced by the
new field-spanning write checks which were enabled recently.

Fix this by replacing the channel_list[1] declaration at the end of
the struct with a flexible array declaration.

Most users of struct brcmf_scan_params_le calculate the size to alloc
using the size of the non flex-array part of the struct + needed extra
space, so they do not care about sizeof(struct brcmf_scan_params_le).

brcmf_notify_escan_complete() however uses the struct on the stack,
expecting there to be room for at least 1 entry in the channel-list
to store the special -1 abort channel-id.

To make this work use an anonymous union with a padding member
added + the actual channel_list flexible array.

Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Franky Lin <franky.lin@xxxxxxxxxxxx>
Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230729140500.27892-1-hdegoede@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 .../net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h  | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h
index 05bd636011ec9..58338b6443f8d 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h
@@ -354,7 +354,12 @@ struct brcmf_scan_params_le {
 				 * fixed parameter portion is assumed, otherwise
 				 * ssid in the fixed portion is ignored
 				 */
-	__le16 channel_list[1];	/* list of chanspecs */
+	union {
+		__le16 padding;	/* Reserve space for at least 1 entry for abort
+				 * which uses an on stack brcmf_scan_params_le
+				 */
+		DECLARE_FLEX_ARRAY(__le16, channel_list);	/* chanspecs */
+	};
 };
 
 struct brcmf_scan_results {
-- 
2.40.1