[PATCH wireless v3] wifi: mac80211: parse wrapper TPE elements without an extension offset

[Zhao Li <enderaoelyther@gmail.com>]

From: Zhao Li <enderaoelyther@gmail.com>

Commit d160663ca2fa ("wifi: mac80211: fix TPE in channel switch wrapper
parsing") replaced cfg80211_find_ext_elem() with for_each_element_id() for
Transmit Power Envelope elements inside a Channel Switch Wrapper, but kept
the offset that skipped the Extension ID. The parser now drops the first
byte of each element and misreads the rest.

ieee80211_parse_tpe() takes a u8 length, so for a zero-length element
0 - 1 wraps around to 255 and the parser reads past the element. Received
beacons are parsed this way when the BSS table is updated, with or without
a connection, so a frame sent over the air can trigger it.

Pass the element body and length unchanged, as for a top-level Transmit
Power Envelope element.

AI assistance was used.

Fixes: d160663ca2fa ("wifi: mac80211: fix TPE in channel switch wrapper parsing")
Cc: stable@vger.kernel.org
Signed-off-by: Zhao Li <enderaoelyther@gmail.com>
---
Changes in v3:
- Send through git send-email; the Gmail connector line-wrapped v1 and
  v2, so neither public revision applies.
- No code changes.

Changes in v2:
- Preserve the author name in the mail metadata; no code changes.

v2: https://lore.kernel.org/linux-wireless/CACHPgzyxGEYJVCyGH6GJBvUdqG8zsfyRn5zxDiuj14tw3byXBw@mail.gmail.com/
v1: https://lore.kernel.org/linux-wireless/CACHPgzwtaykrULWEDNuWU0ZacnNf4s4uSsiYmxE_vJhS4jO0GA@mail.gmail.com/

Tested the in-tree parser with a ten-case KUnit extension under KASAN,
applied identically to the base and fixed kernels. The base fails three
decoding cases and reports a slab-out-of-bounds read for a zero-length
nested TPE. All ten cases pass with the fix, without KASAN reports;
the existing TPE suite also passes on both kernels.

Compile-tested with no new W=1 GCC/Clang, sparse or smatch warnings.

 net/mac80211/parse.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/parse.c b/net/mac80211/parse.c
index f3c5a9f6ec7c..7564d655919f 100644
--- a/net/mac80211/parse.c
+++ b/net/mac80211/parse.c
@@ -698,8 +698,8 @@ _ieee802_11_parse_elems_full(struct ieee80211_elems_parse_params *params,
 			for_each_element_id(subelem, WLAN_EID_TX_POWER_ENVELOPE,
 					    pos, elen)
 				ieee80211_parse_tpe(&elems->csa_tpe,
-						    subelem->data + 1,
-						    subelem->datalen - 1);
+						    subelem->data,
+						    subelem->datalen);
 			break;
 		case WLAN_EID_COUNTRY:
 			elems->country_elem = pos;

base-commit: 831e33ad02ff884ecc793c07a9c9bd9e06941fe5
-- 
2.56.1