[PATCH v3] staging: rtl8723bs: fix protected RX frame validation in decrypt path

["Tianchu Chen" <tianchu.chen@linux.dev>]

From: Tianchu Chen <flynnnchen@tencent.com>

The RX software decrypt path mishandles crafted protected frames from a
malicious AP in two ways:

1) decryptor() never checks that a protected frame is long enough to
hold the 802.11 header plus the per-cipher trailer.  All of
rtw_wep_decrypt(), rtw_tkip_decrypt() and rtw_aes_decrypt() compute

	length = hdr.len - hdrlen - iv_len;

and act on the result, and recvframe_chkmic() similarly computes

	datalen = hdr.len - hdrlen - iv_len - icv_len - 8;

for TKIP (the 8-byte Michael MIC is not accounted for in icv_len).
A frame shorter than hdrlen + iv_len + icv_len (+ 8 for TKIP) underflows
these unsigned subtractions, turning into a ~4 GiB iteration count in
aes_decipher()/arc4_crypt()/rtw_seccalctkipmic() or a ~4 GiB crc32_le()
length, causing out-of-bounds reads/writes of up to ~4 GiB starting from
the rx skb.  Reject such frames in decryptor() before touching the IV;
this covers all three ciphers and the TKIP MIC check, and also keeps the
unconditional iv[3] access within the frame.

2) validate_80211w_mgmt() keeps using the frame - two memcpys through
the stale rx_data pointer and a pkt_len update - before checking
whether decryptor() returned NULL.  On decrypt failure (e.g. a unicast
protected deauth/disassoc/action frame with a bad MIC, which this path
always software-decrypts) the skb has already been freed, so this is a
use-after-free read/write, and the caller's error path frees the frame
a second time, drifting free_recvframe_cnt.  Bail out immediately when
decryptor() fails, freeing the temporary mgmt_DATA buffer first.

Discovered by Atuin - Automated Vulnerability Discovery Engine.

Fixes: 554c0a3abf21 ("staging: Add rtl8723bs sdio wifi driver")
Assisted-by: LLM
Cc: stable@vger.kernel.org
Signed-off-by: Tianchu Chen <flynnnchen@tencent.com>
---
v3: improve formatting.
v2: no code change; adds the real-hardware test report requested for
LLM-assisted staging patches.

Test report
=========================

Victim:   Wintel CX-W8 mini PC (Atom Z3735F, on-board RTL8723BS chip, staging r8723bs,
          Debian 13.6.0/Kernel 6.12.94), bought from the second-hand market for this
          test.
Attacker: ESP32-S3 dev board running custom firmware as a rogue AP. Patching a proprietary
          library is needed. Details available to reviewers upon request.

The decryptor bug is reachable at the association stage: the vulnerable decrypt
path is taken before any key is installed, so the attacker never needs
to pass key verification - the rogue AP's PSK does not need to match
the victim's. Knowing an SSID the victim will auto-join is enough.

Once the victim associates, the rogue AP send 802.11 data frames
with FromDS + Protected bit set and a total length of 24..31 bytes,
i.e. shorter than their own CCMP IV (hdrlen 24 + iv_len 8).  With no
key in the HW CAM the frames reach decryptor() with bdecrypted == 0,
and rtw_aes_decrypt() computes length = (24..31) - 24 - 8, a ~4 GiB
underflow fed straight into aes_decipher().

Result: the victim kernel panics within seconds of association.
Captured via netconsole:

[  939.937797] Oops: general protection fault, probably for non-canonical address 0x6de15a87d1c57856: 0000 [#1] PREEMPT SMP PTI
[  939.938075] CPU: 3 UID: 0 PID: 1637 Comm: Xorg Tainted: G         C         6.12.94+deb13-amd64 #1  Debian 6.12.94-1
[  939.938288] Tainted: [C]=CRAP
[  939.938368] Hardware name: Insyde Intel CX-W8/Intel CX-W8, BIOS M.W8RAAA01 04/17/2015
[  939.938515] RIP: 0010:i915_gem_do_execbuffer+0xbd1/0x2950 [i915]
[  939.939945] Code: e2 fe 48 89 50 20 48 8d 74 24 58 4c 89 e9 48 8d 7c 24 60 44 89 f2 e8 ce c2 ff ff 85 c0 0f 85 9d 03 00 00 49 8b bd b8 00 00 00 <48> 83 bf 50 04 00 00 00 74 31 e8 10 1b 01 00 85 c0 0f 85 91 18 00
[  939.940255] RSP: 0018:ffffccdfc0b17788 EFLAGS: 00010246
[  939.940382] RAX: 0000000000000000 RBX: 0000000000000009 RCX: 00000000fffffff5
[  939.940524] RDX: 0000000000000001 RSI: ffff8c5aa8d4d800 RDI: 6de15a87d1c57406
[  939.940664] RBP: 00000000000001f8 R08: ffff8c5aa92e4a90 R09: ffff8c5aaa953518
[  939.940805] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000003a9
[  939.940942] R13: ffff8c5af99f1680 R14: 0000000000000009 R15: 0000000000000000
[  939.941081] FS:  00007f3856594b00(0000) GS:ffff8c5afb980000(0000) knlGS:0000000000000000
[  939.941238] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  939.941358] CR2: 00007f3856155770 CR3: 000000002b7e6000 CR4: 00000000001026f0
[  939.941500] Call Trace:
[  939.941579]  <TASK>
[  939.941702]  i915_gem_execbuffer2_ioctl+0x13b/0x260 [i915]
[  939.943134]  ? __pfx_i915_gem_execbuffer2_ioctl+0x10/0x10 [i915]
[  939.944543]  drm_ioctl_kernel+0xb0/0x100 [drm]
[  939.945069]  drm_ioctl+0x277/0x4d0 [drm]
[  939.945571]  ? __pfx_i915_gem_execbuffer2_ioctl+0x10/0x10 [i915]
[  939.946997]  __x64_sys_ioctl+0x97/0xc0
[  939.947119]  do_syscall_64+0x87/0x1b0
[  939.947235]  ? timerqueue_del+0x2e/0x50
[  939.947343]  ? tomoyo_init_request_info+0x99/0xc0
[  939.947470]  ? tomoyo_path_number_perm+0x8c/0x1f0
[  939.947589]  ? ww_mutex_lock_interruptible+0x18/0x80
[  939.947725]  ? i915_gem_madvise_ioctl+0x239/0x340 [i915]
[  939.949150]  ? __pfx_i915_gem_madvise_ioctl+0x10/0x10 [i915]
[  939.950571]  ? drm_ioctl_kernel+0xb0/0x100 [drm]
[  939.951086]  ? __check_object_size+0x50/0x210
[  939.955215]  ? _copy_to_user+0x36/0x50
[  939.959506]  ? drm_ioctl+0x2a1/0x4d0 [drm]
[  939.964159]  ? __pfx_i915_gem_madvise_ioctl+0x10/0x10 [i915]
[  939.969804]  ? arch_exit_to_user_mode_prepare.isra.0+0x16/0xa0
[  939.974146]  ? syscall_exit_to_user_mode+0x37/0x1b0
[  939.978488]  ? do_syscall_64+0x93/0x1b0
[  939.982872]  ? arch_exit_to_user_mode_prepare.isra.0+0x16/0xa0
[  939.987300]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  939.991768] RIP: 0033:0x7f385691491b
[  939.996285] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  940.001138] RSP: 002b:00007ffdb0cf6710 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  940.006061] RAX: ffffffffffffffda RBX: 0000564e32defb08 RCX: 00007f385691491b
[  940.011048] RDX: 00007ffdb0cf6790 RSI: 0000000040406469 RDI: 0000000000000013
[  940.016090] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000004
[  940.021150] R10: 0000000000000020 R11: 0000000000000246 R12: 00007ffdb0cf6790
[  940.026256] R13: 0000564e32dc3a50 R14: 00000000000000dc R15: 0000000000000013
[  940.031431]  </TASK>

The oops surfacing in i915 rather than in the driver is expected:
A non-canonical garbage pointer in an unrelated subsystem is the expected
signature of the multi-GB linear decipher starting from the rx skb.

 drivers/staging/rtl8723bs/core/rtw_recv.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 7568fc514d7ce..4756e0fedd46f 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -426,8 +426,21 @@ static union recv_frame *decryptor(struct adapter *padapter, union recv_frame *p
 	u32  res = _SUCCESS;
 
 	if (prxattrib->encrypt > 0) {
-		u8 *iv = precv_frame->u.hdr.rx_data + prxattrib->hdrlen;
+		u8 *iv;
+		u32 min_len = prxattrib->hdrlen + prxattrib->iv_len + prxattrib->icv_len;
 
+		/* TKIP appends an 8-byte Michael MIC that icv_len doesn't account for */
+		if (prxattrib->encrypt == _TKIP_)
+			min_len += 8;
+
+		/* a protected frame must be long enough to hold the IV and ICV/MIC */
+		if (precv_frame->u.hdr.len < min_len) {
+			rtw_free_recvframe(precv_frame,
+					   &padapter->recvpriv.free_recv_queue);
+			return NULL;
+		}
+
+		iv = precv_frame->u.hdr.rx_data + prxattrib->hdrlen;
 		prxattrib->key_index = (((iv[3]) >> 6) & 0x3);
 
 		if (prxattrib->key_index > WEP_KEYS) {
@@ -1395,6 +1408,10 @@ static signed int validate_80211w_mgmt(struct adapter *adapter, union recv_frame
 			if (!mgmt_DATA)
 				goto validate_80211w_fail;
 			precv_frame = decryptor(adapter, precv_frame);
+			if (!precv_frame) {
+				kfree(mgmt_DATA);
+				goto validate_80211w_fail;
+			}
 			/* save actual management data frame body */
 			memcpy(mgmt_DATA, ptr + pattrib->hdrlen + pattrib->iv_len, data_len);
 			/* overwrite the iv field */
@@ -1402,8 +1419,6 @@ static signed int validate_80211w_mgmt(struct adapter *adapter, union recv_frame
 			/* remove the iv and icv length */
 			pattrib->pkt_len = pattrib->pkt_len - pattrib->iv_len - pattrib->icv_len;
 			kfree(mgmt_DATA);
-			if (!precv_frame)
-				goto validate_80211w_fail;
 		} else if (is_multicast_ether_addr(GetAddr1Ptr(ptr)) &&
 			(subtype == WIFI_DEAUTH || subtype == WIFI_DISASSOC)) {
 			signed int BIP_ret = _SUCCESS;
-- 
2.51.0