rsi: Fix out-of-bounds read in rsi_read_pkt()

rsi_get_* functions rely on an offset variable from usb
input. The size of usb input is RSI_MAX_RX_USB_PKT_SIZE(3000),
while 2-byte offset can be up to 0xFFFF. Thus a large offset
can cause out-of-bounds read.

The patch adds a bound checking condition when rcv_pkt_len is 0,
indicating it's USB. It's unclear whether this is triggerable
from other type of bus. The following check might help in that case.
offset > rcv_pkt_len - FRAME_DESC_SZ

The bug is trigerrable with conpromised/malfunctioning USB devices.
I tested the patch with the crashing input and got no more bug report.

Attached is the KASAN report from fuzzing.

BUG: KASAN: slab-out-of-bounds in rsi_read_pkt+0x42e/0x500 [rsi_91x]
Read of size 2 at addr ffff888019439fdb by task RX-Thread/227

CPU: 0 PID: 227 Comm: RX-Thread Not tainted 5.6.0 #66
Call Trace:
 dump_stack+0x76/0xa0
 print_address_description.constprop.0+0x16/0x200
 ? rsi_read_pkt+0x42e/0x500 [rsi_91x]
 ? rsi_read_pkt+0x42e/0x500 [rsi_91x]
 __kasan_report.cold+0x37/0x7c
 ? rsi_read_pkt+0x42e/0x500 [rsi_91x]
 kasan_report+0xe/0x20
 rsi_read_pkt+0x42e/0x500 [rsi_91x]
 rsi_usb_rx_thread+0x1b1/0x2fc [rsi_usb]
 ? rsi_probe+0x16a0/0x16a0 [rsi_usb]
 ? _raw_spin_lock_irqsave+0x7b/0xd0
 ? _raw_spin_trylock_bh+0x120/0x120
 ? __wake_up_common+0x10b/0x520
 ? rsi_probe+0x16a0/0x16a0 [rsi_usb]
 kthread+0x2b5/0x3b0
 ? kthread_create_on_node+0xd0/0xd0
 ret_from_fork+0x22/0x40

Reported-by: Brendan Dolan-Gavitt <brendandg@nyu.edu>
Signed-off-by: Zekun Shen <bruceshenzk@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/YXxXS4wgu2OsmlVv@10-18-43-117.dynapool.wireless.nyu.edu

drivers/net/wireless/rsi/rsi_91x_main.c

@@ -23,6 +23,7 @@
 #include "rsi_common.h"
 #include "rsi_coex.h"
 #include "rsi_hal.h"
+#include "rsi_usb.h"
 
 u32 rsi_zone_enabled = /* INFO_ZONE |
 			INIT_ZONE |
@@ -168,6 +169,9 @@ int rsi_read_pkt(struct rsi_common *common, u8 *rx_pkt, s32 rcv_pkt_len)
 		frame_desc = &rx_pkt[index];
 		actual_length = *(u16 *)&frame_desc[0];
 		offset = *(u16 *)&frame_desc[2];
+		if (!rcv_pkt_len && offset >
+			RSI_MAX_RX_USB_PKT_SIZE - FRAME_DESC_SZ)
+			goto fail;
 
 		queueno = rsi_get_queueno(frame_desc, offset);
 		length = rsi_get_length(frame_desc, offset);

drivers/net/wireless/rsi/rsi_91x_usb.c

@@ -330,7 +330,6 @@ static int rsi_rx_urb_submit(struct rsi_hw *adapter, u8 ep_num, gfp_t mem_flags)
 	struct sk_buff *skb;
 	u8 dword_align_bytes = 0;
 
-#define RSI_MAX_RX_USB_PKT_SIZE	3000
 	skb = dev_alloc_skb(RSI_MAX_RX_USB_PKT_SIZE);
 	if (!skb)
 		return -ENOMEM;

drivers/net/wireless/rsi/rsi_usb.h

@@ -44,6 +44,8 @@
 #define RSI_USB_BUF_SIZE	     4096
 #define RSI_USB_CTRL_BUF_SIZE	     0x04
 
+#define RSI_MAX_RX_USB_PKT_SIZE	3000
+
 struct rx_usb_ctrl_block {
 	u8 *data;
 	struct urb *rx_urb;