Re: [dpdk-dev] [PATCH] net/failsafe: fix parameters parsing

[Gaëtan Rivet]

Hi Matan,

Thanks for spotting the bug.

On Thu, Aug 17, 2017 at 05:19:41PM +0300, Matan Azrad wrote:
> The corrupted code used wrongly snprintf return value as the
> number of characters actually copied, in spite of the meanning
> is the number of characters which would be generated for the
> given input.
> 
> It caused to remain zerod bytes between the failsafe command line
> non sub device parameters indicates end of string.
> 
> Hence, when rte_kvargs_parse tried to parse all parameters, it
> got end of string after the first one and the others weren't parsed.
> 
> So, if the mac parameters was the first in command line it was
> taken while hotplug_poll was left default, and vice versa.
> 
> The fix updates the buffer index by dedicated variable contains
> the copy size, by the way uses memcpy instead of snprintf
> which is good enouth for this copy scenario.

Actually snprintf should still be used.

> 
> Fixes: a46f8d584eb8 ("net/failsafe: add fail-safe PMD")
> Cc: sta...@dpdk.org
> 
> Signed-off-by: Matan Azrad <ma...@mellanox.com>
> ---
>  drivers/net/failsafe/failsafe_args.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/failsafe/failsafe_args.c 
> b/drivers/net/failsafe/failsafe_args.c
> index 1f22416..0a98b04 100644
> --- a/drivers/net/failsafe/failsafe_args.c
> +++ b/drivers/net/failsafe/failsafe_args.c
> @@ -271,7 +271,7 @@ static int
>  fs_remove_sub_devices_definition(char params[DEVARGS_MAXLEN])
>  {
>       char buffer[DEVARGS_MAXLEN] = {0};
> -     size_t a, b;
> +     size_t a, b, temp;

temp is not descriptive enough.
You are declaring this variable here because you want to re-use it
instead of `start`. This is an overreach however, this fix must be
restricted to the actual bug.

>       int i;
>  
>       a = 0;
> @@ -286,12 +286,14 @@ fs_remove_sub_devices_definition(char 
> params[DEVARGS_MAXLEN])
>                       ERROR("Invalid parameter");
>                       return -EINVAL;
>               }
> -             if (params[b] == ',' || params[b] == '\0')

Declare the temporary variable in this scope, with a descriptive name
such as "len", "length", "param_len" or something close.

> -                     i += snprintf(&buffer[i], b - a + 1, "%s", &params[a]);
> -             if (params[b] == '(') {
> -                     size_t start = b;
> +             if (params[b] == ',' || params[b] == '\0') {
> +                     temp = b - a + 1;

The value here should be "b - a".
If a != 0 however, then we are parsing a new parameter and buffer
already contains at least one. A comma should be added to separate the
two.

An example might clarify what I mean:

                if (params[b] == ',' || params[b] == '\0') {
                        size_t param_len = b - a;

                        if (a)
                                param_len += 1;
                        snprintf(&buffer[i], param_len + 1, "%s%s",
                                 a ? "," : "", &params[a]);
                        i += param_len;
                }

The conditionals about `a` are ugly however, if you find a better way to write
those you are most welcome :).

> +                     memcpy(&buffer[i], &params[a], temp);
> +                     i += temp;
> +             } else if (params[b] == '(') {
> +                     temp = b;
>                       b += closing_paren(&params[b]);
> -                     if (b == start)

The changes should be limited to the actual bug. No need to change this.

> +                     if (b == temp)
>                               return -EINVAL;
>                       b += 1;
>                       if (params[b] == '\0')
> -- 
> 2.7.4
> 

Thanks again for the debug and sorry for being nitpicky.

-- 
Gaëtan Rivet
6WIND