[PATCH AUTOSEL 6.9 24/44] wifi: mac80211: fix UBSAN noise in ieee80211_prep_hw_scan()

Sasha Levin
2024-06-17T13:21:46Z

From: Dmitry Antipov <dmantipov@yandex.ru>

[ Upstream commit 92ecbb3ac6f3fe8ae9edf3226c76aa17b6800699 ]

When testing the previous patch with CONFIG_UBSAN_BOUNDS, I've
noticed the following:

UBSAN: array-index-out-of-bounds in net/mac80211/scan.c:372:4
index 0 is out of range for type 'struct ieee80211_channel *[]'
CPU: 0 PID: 1435 Comm: wpa_supplicant Not tainted 6.9.0+ #1
Hardware name: LENOVO 20UN005QRT/20UN005QRT <...BIOS details...>
Call Trace:
<TASK>
dump_stack_lvl+0x2d/0x90
__ubsan_handle_out_of_bounds+0xe7/0x140
? timerqueue_add+0x98/0xb0
ieee80211_prep_hw_scan+0x2db/0x480 [mac80211]
? __kmalloc+0xe1/0x470
__ieee80211_start_scan+0x541/0x760 [mac80211]
rdev_scan+0x1f/0xe0 [cfg80211]
nl80211_trigger_scan+0x9b6/0xae0 [cfg80211]
...<the rest is not too useful...>

Since '__ieee80211_start_scan()' leaves 'hw_scan_req->req.n_channels'
uninitialized, actual boundaries of 'hw_scan_req->req.channels' can't
be checked in 'ieee80211_prep_hw_scan()'. Although an initialization
of 'hw_scan_req->req.n_channels' introduces some confusion around
allocated vs. used VLA members, this shouldn't be a problem since
everything is correctly adjusted soon in 'ieee80211_prep_hw_scan()'.

Cleanup 'kmalloc()' math in '__ieee80211_start_scan()' by using the
convenient 'struct_size()' as well.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Link: https://msgid.link/20240517153332.18271-2-dmantipov@yandex.ru
[improve (imho) indentation a bit]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/mac80211/scan.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 3da1c5c450358..8ecc4b710b0e6 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -744,15 +744,21 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
local->hw_scan_ies_bufsize *= n_bands;
}

- local->hw_scan_req = kmalloc(
- sizeof(*local->hw_scan_req) +
- req->n_channels * sizeof(req->channels[0]) +
- local->hw_scan_ies_bufsize, GFP_KERNEL);
+ local->hw_scan_req = kmalloc(struct_size(local->hw_scan_req,
+ req.channels,
+ req->n_channels) +
+ local->hw_scan_ies_bufsize,
+ GFP_KERNEL);
if (!local->hw_scan_req)
return -ENOMEM;

local->hw_scan_req->req.ssids = req->ssids;
local->hw_scan_req->req.n_ssids = req->n_ssids;
+ /* None of the channels are actually set
+ * up but let UBSAN know the boundaries.
+ */
+ local->hw_scan_req->req.n_channels = req->n_channels;
+
ies = (u8 *)local->hw_scan_req +
sizeof(*local->hw_scan_req) +
req->n_channels * sizeof(req->channels[0]);
--
2.43.0