linux-kernel - RE: [PATCH] wifi: cisco: do not assign -1 to unsigned char

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Message-ID: <6a1652ab408d4c5d8ba754f35680e792@AcuMS.aculab.com>
Date:   Tue, 25 Oct 2022 10:11:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Jason A. Donenfeld'" <Jason@...c4.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Kalle Valo <kvalo@...nel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: RE: [PATCH] wifi: cisco: do not assign -1 to unsigned char

From: Jason A. Donenfeld
> Sent: 24 October 2022 17:29
> 
> With char becoming unsigned by default, and with `char` alone being
> ambiguous and based on architecture, we get a warning when assigning the
> unchecked output of hex_to_bin() to that unsigned char. Mark `key` as a
> `u8`, which matches the struct's type, and then check each call to
> hex_to_bin() before casting.
> 
> Cc: Kalle Valo <kvalo@...nel.org>
> Cc: linux-wireless@...r.kernel.org
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  drivers/net/wireless/cisco/airo.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/wireless/cisco/airo.c b/drivers/net/wireless/cisco/airo.c
> index 10daef81c355..fb2c35bd73bb 100644
> --- a/drivers/net/wireless/cisco/airo.c
> +++ b/drivers/net/wireless/cisco/airo.c
> @@ -5232,7 +5232,7 @@ static int get_wep_tx_idx(struct airo_info *ai)
>  	return -1;
>  }
> 
> -static int set_wep_key(struct airo_info *ai, u16 index, const char *key,
> +static int set_wep_key(struct airo_info *ai, u16 index, const u8 *key,
>  		       u16 keylen, int perm, int lock)
>  {
>  	static const unsigned char macaddr[ETH_ALEN] = { 0x01, 0, 0, 0, 0, 0 };
> @@ -5283,7 +5283,7 @@ static void proc_wepkey_on_close(struct inode *inode, struct file *file)
>  	struct net_device *dev = pde_data(inode);
>  	struct airo_info *ai = dev->ml_priv;
>  	int i, rc;
> -	char key[16];
> +	u8 key[16];
>  	u16 index = 0;
>  	int j = 0;
> 
> @@ -5311,12 +5311,22 @@ static void proc_wepkey_on_close(struct inode *inode, struct file *file)
>  	}
> 
>  	for (i = 0; i < 16*3 && data->wbuffer[i+j]; i++) {
> +		int val;
> +
> +		if (i % 3 == 2)
> +			continue;
> +
> +		val = hex_to_bin(data->wbuffer[i+j]);
> +		if (val < 0) {
> +			airo_print_err(ai->dev->name, "WebKey passed invalid key hex");
> +			return;
> +		}
>  		switch(i%3) {
>  		case 0:
> -			key[i/3] = hex_to_bin(data->wbuffer[i+j])<<4;
> +			key[i/3] = (u8)val << 4;
>  			break;
>  		case 1:
> -			key[i/3] |= hex_to_bin(data->wbuffer[i+j]);
> +			key[i/3] |= (u8)val;
>  			break;
>  		}
>  	}

That is about the crappiest loop I've seen.
I was just going to point out that the (u8) casts aren't needed.
Something like:
	for (i = 0, buf = data->wbuffer + j; i < 16; i++, buf += 3) {
		int val;
		if (!buf[0] || !buf[1])
			break;
		val = hex_to_bin(buf[0]) | hex_to_bin(buf[1]) << 8;
		if (val < 0) {
			airo_print_err(ai->dev->name, "WebKey passed invalid key hex");
			return;
		}
		key[i] = val;
		if (!buf[2])
			break;
	}

Although there should be a check for buf[2] being valid.
Any I worry about exactly what happens if there aren't 16 full bytes.

	David

		

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