RE: [PATCH net-next 3/9] s390/qeth: clean up string ops in qeth_l3_parse_ipatoe()

[David Laight <David.Laight@ACULAB.COM>]

From: Julian Wiedmann
> Sent: 23 September 2020 09:37
> 
> Indicate the max number of to-be-parsed characters, and avoid copying
> the address sub-string.
> 
> Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
> ---
>  drivers/s390/net/qeth_l3_sys.c | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/s390/net/qeth_l3_sys.c b/drivers/s390/net/qeth_l3_sys.c
> index ca9c95b6bf35..05fa986e30fc 100644
> --- a/drivers/s390/net/qeth_l3_sys.c
> +++ b/drivers/s390/net/qeth_l3_sys.c
> @@ -409,21 +409,22 @@ static ssize_t qeth_l3_dev_ipato_add4_show(struct device *dev,
>  static int qeth_l3_parse_ipatoe(const char *buf, enum qeth_prot_versions proto,
>  		  u8 *addr, int *mask_bits)
>  {
> -	const char *start, *end;
> -	char *tmp;
> -	char buffer[40] = {0, };
> +	const char *start;
> +	char *sep, *tmp;
> +	int rc;
> 
> -	start = buf;
> -	/* get address string */
> -	end = strchr(start, '/');
> -	if (!end || (end - start >= 40)) {
> +	/* Expected input pattern: %addr/%mask */
> +	sep = strnchr(buf, 40, '/');
> +	if (!sep)
>  		return -EINVAL;
> -	}
> -	strncpy(buffer, start, end - start);
> -	if (qeth_l3_string_to_ipaddr(buffer, proto, addr)) {
> -		return -EINVAL;
> -	}
> -	start = end + 1;
> +
> +	/* Terminate the %addr sub-string, and parse it: */
> +	*sep = '\0';

Is it valid to write into the input buffer here?

> +	rc = qeth_l3_string_to_ipaddr(buf, proto, addr);
> +	if (rc)
> +		return rc;
> +
> +	start = sep + 1;
>  	*mask_bits = simple_strtoul(start, &tmp, 10);

The use of strnchr() rather implies that the input
buffer may not be '\0' terminated.
If that is true then you've just run off the end of the
input buffer.

>  	if (!strlen(start) ||
>  	    (tmp == start) ||

Hmmm... delete the strlen() clause.
It ought to test start[0], but the 'tmp == start' test
covers that case.

I don't understand why simple_strtoul() is deprecated.
I don't recall any of the replacements returning the
address of the terminating character.

	David

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