[U-Boot] [PATCH v2] efi_loader: fix off-by-one bug in efi_get_variable

[Heinrich Schuchardt]

On 05/10/2018 04:25 AM, Ivan Gorinov wrote:
> efi_get_variable() always stores an extra zero byte after the output data.
> When the returned data size matches the output buffer size, the extra zero
> byte is stored past the end of the output buffer.
> 
> Signed-off-by: Ivan Gorinov <ivan.gorinov at intel.com>
> ---
>  lib/efi_loader/efi_variable.c | 64 +++++++++++++++++++++----------------------
>  1 file changed, 32 insertions(+), 32 deletions(-)
> 
> diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
> index 6c177da..b1e6a73 100644
> --- a/lib/efi_loader/efi_variable.c
> +++ b/lib/efi_loader/efi_variable.c
> @@ -50,7 +50,7 @@
>  	(strlen("efi_xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx_") + \
>  		(MAX_VAR_NAME * MAX_UTF8_PER_UTF16))
>  
> -static int hex(unsigned char ch)
> +static int hex(char ch)
>  {
>  	if (ch >= 'a' && ch <= 'f')
>  		return ch-'a'+10;
> @@ -61,44 +61,41 @@ static int hex(unsigned char ch)
>  	return -1;
>  }
>  
> -static const char *hex2mem(u8 *mem, const char *hexstr, int count)
> +static int hex2mem(u8 *mem, const char *hexstr, int size)

Why do you need size if hexstr is zero terminated?

>  {
> -	memset(mem, 0, count/2);
> +	u8 data;
> +	int nibble;
> +	char ch;
> +	int i, k;
>  
> -	do {
> -		int nibble;
> +	memset(mem, 0, size);
>  
> -		*mem = 0;
> +	for (i = 0; i < size; i += 1) {
People are used to reading ++i or i++ for simple incrementation.

> +		data = 0;
> +		for (k = 0; k < 2; k += 1) {

Why use nested loops? That neither makes the code easier to read nor faster.

Why all the changes if you still do not throw an error if hexstr has an
uneven number of nibbles?

Best regards

Heinrich


> +			ch = *(hexstr++);
>  
> -		if (!count || !*hexstr)
> -			break;
> -
> -		nibble = hex(*hexstr);
> -		if (nibble < 0)
> -			break;
> -
> -		*mem = nibble;
> -		count--;
> -		hexstr++;
> -
> -		if (!count || !*hexstr)
> -			break;
> +			if (!ch) {
> +				if (k == 0)
> +					return i;
> +				else
> +					return -1;
> +			}
>  
> -		nibble = hex(*hexstr);
> -		if (nibble < 0)
> -			break;
> +			nibble = hex(ch);
> +			if (nibble < 0)
> +				return -1;
>  
> -		*mem = (*mem << 4) | nibble;
> -		count--;
> -		hexstr++;
> -		mem++;
> +			hexstr++;
>  
> -	} while (1);
> +			data <<= 4;
> +			data |= nibble;
>  
> -	if (*hexstr)
> -		return hexstr;
> +		}
> +		mem[i] = data;
> +	}
>  
> -	return NULL;
> +	return i;
>  }
>  
>  static char *mem2hex(char *hexstr, const u8 *mem, int count)
> @@ -210,8 +207,11 @@ efi_status_t EFIAPI efi_get_variable(s16 *variable_name,
>  	if ((s = prefix(val, "(blob)"))) {
>  		unsigned len = strlen(s);
>  
> +		if (len & 1)
> +			return EFI_EXIT(EFI_DEVICE_ERROR);
> +
>  		/* two characters per byte: */
> -		len = DIV_ROUND_UP(len, 2);
> +		len /= 2;
>  		*data_size = len;
>  
>  		if (in_size < len)
> @@ -220,7 +220,7 @@ efi_status_t EFIAPI efi_get_variable(s16 *variable_name,
>  		if (!data)
>  			return EFI_EXIT(EFI_INVALID_PARAMETER);
>  
> -		if (hex2mem(data, s, len * 2))
> +		if (hex2mem(data, s, len) != len)
>  			return EFI_EXIT(EFI_DEVICE_ERROR);
>  
>  		debug("%s: got value: \"%s\"\n", __func__, s);
>