Re: [PATCH] tracing: Add *iter check for NULL

[Steven Rostedt]

On Wed,  1 Jun 2016 16:31:10 +0800
zhengjun.xing@xxxxxxxxx wrote:

> From: xingzhen <zhengjun.xing@xxxxxxxxx>
> 
> 3debb0a9ddb adding a "__used" to the variable in the
> __trace_printk_fmt section. Sometimes it will cause
> *iter to be NULL, then strcmp in lookup_format and
> strcpy in hold_module_trace_bprintk_format will panic.

Could you show an example of this happening?

> 
> Signed-off-by: xingzhen <zhengjun.xing@xxxxxxxxx>
> ---
>  kernel/trace/trace_printk.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
> index f96f038..82ecfb5 100644
> --- a/kernel/trace/trace_printk.c
> +++ b/kernel/trace/trace_printk.c
> @@ -55,6 +55,8 @@ void hold_module_trace_bprintk_format(const char **start, const char **end)
>  
>  	mutex_lock(&btrace_mutex);
>  	for (iter = start; iter < end; iter++) {
> +		if (!*iter)
> +			goto err;
>  		struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter);

First, you can't place logic before a declaration. Not all compilers
will allow that.

Also, do we really want to error on this or just skip it? Because it
will miss out on all other trace_printks in the module.

-- Steve


>  		if (tb_fmt) {
>  			*iter = tb_fmt->fmt;
> @@ -75,6 +77,7 @@ void hold_module_trace_bprintk_format(const char **start, const char **end)
>  		*iter = fmt;
>  
>  	}
> +err:
>  	mutex_unlock(&btrace_mutex);
>  }
>