linux-kernel - Re: [PATCH] tools lib traceevent: Fix missing equality check for strcmp

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Message-ID: <20190409092122.2e8f62f0@gandalf.local.home>
Date:   Tue, 9 Apr 2019 09:21:22 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Rikard Falkeborn <rikard.falkeborn@...il.com>
Cc:     linux-kernel@...r.kernel.org, acme@...hat.com,
        tstoyanov@...are.com,
        Linux Trace Devel <linux-trace-devel@...r.kernel.org>
Subject: Re: [PATCH] tools lib traceevent: Fix missing equality check for
 strcmp


Hi Rikard,

On Tue,  9 Apr 2019 11:15:29 +0200
Rikard Falkeborn <rikard.falkeborn@...il.com> wrote:

> There was a missing comparison with 0 when checking if type is "s64" or
> "u64". Therefore, the body of the if-statement was entered if "type" was
> "u64" or not "s64", which made the first strcmp() redundant since if
> type is "u64", it's not "s64".
> 
> If type is "s64", the body of the if-statement is not entered but since the
> remainder of the function consists of if-statements which will not be
> entered if type is "s64", we will just return "val", which is correct,
> albeit at the cost of a few more calls to strcmp(), i.e., it will behave
> just as if the if-statement was entered.
> 
> If type is neither "s64" or "u64", the body of the if-statement will be
> entered incorrectly and "val" returned. This means that any type that is
> checked after "s64" and "u64" is handled the same way as "s64" and
> "u64", i.e., the limiting of "val" to fit in for example "s8" is never
> reached.
> 
> This was introduced in the kernel tree when the sources were copied from
> trace-cmd in commit f7d82350e597 ("tools/events: Add files to create
> libtraceevent.a"), and in the trace-cmd repo in 1cdbae6035cei ("Implement
> typecasting in parser") when the function was introduced, i.e., it has
> always behaved the wrong way.
> 
> Detected by cppcheck.

Nice. Thanks for this.

> 
> Fixes: f7d82350e597 ("tools/events: Add files to create libtraceevent.a")
> Signed-off-by: Rikard Falkeborn <rikard.falkeborn@...il.com>

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Arnaldo,

Care to pull this in?

Thanks!

-- Steve

> ---
> I have only compile tested the patch but it should be correct. I don't
> know if any other problems will surface due to this though.
> ---
>  tools/lib/traceevent/event-parse.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index 87494c7c619d..981c6ce2da2c 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -2233,7 +2233,7 @@ eval_type_str(unsigned long long val, const char *type, int pointer)
>  		return val & 0xffffffff;
>  
>  	if (strcmp(type, "u64") == 0 ||
> -	    strcmp(type, "s64"))
> +	    strcmp(type, "s64") == 0)
>  		return val;
>  
>  	if (strcmp(type, "s8") == 0)