Re: [PATCH] brcmfmac: Fixes potential buffer overflow in 'brcmf_fweh_event_worker'

[Arend Van Spriel <aspriel@gmail.com>]

On 10/20/2022 3:49 AM, Dokyung Song wrote:
> This patch fixes an intra-object buffer overflow in brcmfmac that occurs
> when the device provides a 'bsscfgidx' equal to or greater than the
> buffer size. The patch adds a check that leads to a safe failure if that
> is the case.
> 
> Found by a modified version of syzkaller.
> 
> UBSAN: array-index-out-of-bounds in drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
> index 52 is out of range for type 'brcmf_if *[16]'
> CPU: 0 PID: 1898 Comm: kworker/0:2 Tainted: G           O      5.14.0+ #132

[...]

> Kernel panic - not syncing: Fatal exception
> 
> Reported-by: Dokyung Song <dokyungs@yonsei.ac.kr>
> Reported-by: Jisoo Jang <jisoo.jang@yonsei.ac.kr>
> Reported-by: Minsuk Kang <linuxlovemin@yonsei.ac.kr>

Not sure what the rules are for using 'Reported-by' tag, but it looks a 
bit odd. I leave it to the wireless maintainer.

Reviewed-by: Arend van Spriel <aspriel@gmail.com>
> Signed-off-by: Dokyung Song <dokyung.song@gmail.com>
> ---
>   drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
> index bc3f4e4edcdf..e035e9c5a1fa 100644
> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
> @@ -255,10 +255,15 @@ static void brcmf_fweh_event_worker(struct work_struct *work)
>   			goto event_free;
>   		}
>   
> -		if (event->code == BRCMF_E_TDLS_PEER_EVENT)
> +		if (event->code == BRCMF_E_TDLS_PEER_EVENT) {
>   			ifp = drvr->iflist[0];
> -		else
> +		} else {
> +			if (emsg.bsscfgidx >= BRCMF_MAX_IFS) {
> +				bphy_err(drvr, "invalid bsscfg index: %u\n", emsg.bsscfgidx);
> +				goto event_free;
> +			}

probably better to do the validation before any other handling. So right 
after converting the event message at line 245

https://elixir.bootlin.com/linux/latest/source/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c#L245

>   			ifp = drvr->iflist[emsg.bsscfgidx];
> +		}
>   		err = brcmf_fweh_call_event_handler(drvr, ifp, event->code,
>   						    &emsg, event->data);
>   		if (err) {