Re: [dpdk-dev] [PATCH v1] lib/cmdline: init parse result memory

[Olivier MATZ <olivier.matz@6wind.com>]

Hi,

On Fri, Dec 08, 2017 at 04:04:33PM +0100, Adrien Mazarguil wrote:
> On Fri, Dec 08, 2017 at 02:51:15PM +0100, Olivier MATZ wrote:
> > On Fri, Dec 08, 2017 at 01:27:26PM +0100, Adrien Mazarguil wrote:
> > > On Fri, Dec 08, 2017 at 03:02:44PM +0800, Xueming Li wrote:
> > > > Initialize binary result memory before parsing to avoid garbage in
> > > > parsing result.
> > > > 
> > > > Signed-off-by: Xueming Li <xuemingl@mellanox.com>
> > > 
> > > Since you chose to move the break statement, maybe the original commit
> > > mentioned in my previous message (9b3fbb051d2e "cmdline: fix parsing") can
> > > be reverted afterward? I think it makes tmp_result redundant.
> > > 
> > > Wenzhuo, as the author of that commit, can you confirm?
> > > 
> > > Olivier, no problem with breaking the loop immediately after the first
> > > successful match_inst() call instead of the last one? (I don't see why it
> > > would be an issue but I may have missed something)
> > 
> > Moving the break will change the behavior, it will never detect
> > ambiguous commands (i.e when several commands match the same input).
> > So I think we should not do it.
> > 
> > IMO, only the memset() is enough.
> 
> I agree it should be, however as reported by Xueming doing so somehow breaks
> the flow command. In my previous reply I assumed that was caused by clearing
> the result buffer of prior successful calls in cmdline_parse(), I just
> checked and it appears not to be the case. Wenzhuo's patch works fine.
> 
> The root cause is actually the flow command stores internal buffer addresses
> in the output buffer, which happens to be tmp_result.buf since commit
> 9b3fbb051d2e.
> 
> When match_inst() returns successfully, tmp_result.buf is copied to
> result.buf and the contents of tmp_result.buf are discarded by the next call
> to match_inst(). Addresses stored inside result.buf still refer to locations
> inside tmp_result.buf, memset()'ing that region only makes that bug manifest
> itself.
> 
> Another suggestion to address the underlying issue before adding memset():
> 
> diff --git a/lib/librte_cmdline/cmdline_parse.c b/lib/librte_cmdline/cmdline_parse.c
> index 205f243..15a3482 100644
> --- a/lib/librte_cmdline/cmdline_parse.c
> +++ b/lib/librte_cmdline/cmdline_parse.c
> @@ -254,7 +254,7 @@ cmdline_parse(struct cmdline *cl, const char * buf)
>  	union {
>  		char buf[CMDLINE_PARSE_RESULT_BUFSIZE];
>  		long double align; /* strong alignment constraint for buf */
> -	} result, tmp_result;
> +	} result, result_ok;
>  	void (*f)(void *, struct cmdline *, void *) = NULL;
>  	void *data = NULL;
>  	int comment = 0;
> @@ -315,16 +315,13 @@ cmdline_parse(struct cmdline *cl, const char * buf)
>  		debug_printf("INST %d\n", inst_num);
>  
>  		/* fully parsed */
> -		tok = match_inst(inst, buf, 0, tmp_result.buf,
> -				 sizeof(tmp_result.buf));
> +		tok = match_inst(inst, buf, 0, result.buf, sizeof(result.buf));
>  
>  		if (tok > 0) /* we matched at least one token */
>  			err = CMDLINE_PARSE_BAD_ARGS;
>  
>  		else if (!tok) {
>  			debug_printf("INST fully parsed\n");
> -			memcpy(&result, &tmp_result,
> -			       sizeof(result));
>  			/* skip spaces */
>  			while (isblank2(*curbuf)) {
>  				curbuf++;
> @@ -344,6 +341,7 @@ cmdline_parse(struct cmdline *cl, const char * buf)
>  					break;
>  				}
>  			}
> +			result_ok = result;
>  		}
>  
>  		inst_num ++;
> @@ -352,6 +350,7 @@ cmdline_parse(struct cmdline *cl, const char * buf)
>  
>  	/* call func */
>  	if (f) {
> +		result = result_ok;
>  		f(result.buf, cl, data);
>  	}
> 

In addition to the memset() at the beginning of match_inst(), it looks
good to me.

A particular attention should be paid to the explanation of the issue
and its solution in the commit log :)