linux-kernel - Re: [PATCH] staging: rtl8192u: change get_key functions to return 0 instead of -1

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Message-ID: <3183776.G96rZvMJ2N@leap>
Date:   Wed, 20 Apr 2022 16:52:36 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        outreachy@...ts.linux.dev, Rebecca Mckeever <remckee0@...il.com>
Subject: Re: [PATCH] staging: rtl8192u: change get_key functions to return 0 instead of -1

On mercoledì 20 aprile 2022 14:23:28 CEST Rebecca Mckeever wrote:
> Currently, these three get_key functions return -1 when the provided len
> value is less a specific key length value, which can result in buffer
> overflow depending on how the returned value is used. These functions are
> used in three places in ieee80211/ieee80211_wx.c:
> 
>   ieee80211_wx_get_encode() :
>     The behavior of this function will be unchanged.
> 
>   ieee80211_wx_get_encode_ext() :
>     The result of the get_key function is written to ext->key_len,
>     resulting in a buffer overflow if the result is negative.
> 
>   ieee80211_wx_set_encode() :
>     The behavior of this function will change. When len is less than the
>     key length value, it will set a default key of all 0.
> 
> Suggested-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Rebecca Mckeever <remckee0@...il.com>
> ---
>  drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c | 2 +-
>  drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_tkip.c | 2 +-
>  drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_wep.c  | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)

I was not able to find the message where Dan suggested this solution. 
However it looks that we actually have problems in those callers when they 
get '-1' as the return code.

I didn't look at the code with much attention but I think that returning 
'0' to signal errors is not so good.

If I'm not missing something from the context, I'd rather return '-EINVAL' 
and change the callers to check for this specific error that would signal 
we have "len less than a specific len value". If so, act in accordance to 
the returned -EINVAL.

For example, in a caller you may test:

if (ext->key_len == -EINVAL || <some other test, if required>)
        <error path>
<success path>

Just my thoughts, but, as I said, I haven't checked carefully neither the 
callers nor the called functions. Maybe that returning '0' is the better 
solution, but it usually means that we have no errors. 

However, I'm 100% sure that, if Dan suggested this specific solution, there 
must be good reasons behind. If so, your changes are good :)

Thanks,

Fabio M. De Francesco

> 
> diff --git a/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c b/
drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c
> index 101c28265e91..f17d07dad56d 100644
> --- a/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c
> +++ b/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c
> @@ -362,7 +362,7 @@ static int ieee80211_ccmp_get_key(void *key, int len, 
u8 *seq, void *priv)
>  	struct ieee80211_ccmp_data *data = priv;
>  
>  	if (len < CCMP_TK_LEN)
> -		return -1;
> +		return 0;
>  
>  	if (!data->key_set)
>  		return 0;
> diff --git a/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_tkip.c b/
drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_tkip.c
> index 689d8843f538..7b120b8cb982 100644
> --- a/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_tkip.c
> +++ b/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_tkip.c
> @@ -637,7 +637,7 @@ static int ieee80211_tkip_get_key(void *key, int len, 
u8 *seq, void *priv)
>  	struct ieee80211_tkip_data *tkey = priv;
>  
>  	if (len < TKIP_KEY_LEN)
> -		return -1;
> +		return 0;
>  
>  	if (!tkey->key_set)
>  		return 0;
> diff --git a/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_wep.c b/
drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_wep.c
> index 8a51ea1dd6e5..a2cdf3bfd1a4 100644
> --- a/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_wep.c
> +++ b/drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_wep.c
> @@ -201,7 +201,7 @@ static int prism2_wep_get_key(void *key, int len, u8 
*seq, void *priv)
>  	struct prism2_wep_data *wep = priv;
>  
>  	if (len < wep->key_len)
> -		return -1;
> +		return 0;
>  
>  	memcpy(key, wep->key, wep->key_len);
>  
> -- 
> 2.32.0
> 
> 
>