Subject: Re: [PATCH] rsi_usb: Fix out-of-bounds read in rsi_read_pkt

From: Kalle Valo <[email-masked]>
Date: Mon, 01 Nov 2021 16:07:37 +0200

Zekun Shen <[email-masked]> writes:

> 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: Zekun Shen <[email-masked]>

You are the author, no need to have your name in Reported-by.

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