Re: [PATCH v1 04/12] dyndbg: add 2 trace-events: pr_debug, dev_dbg

[Steven Rostedt]

On Fri,  3 Nov 2023 14:10:03 +0100
Łukasz Bartosik <lb@xxxxxxxxxxxx> wrote:

> +/* capture pr_debug() callsite descriptor and message */
> +TRACE_EVENT(prdbg,
> +	    TP_PROTO(const struct _ddebug *desc, const char *text, size_t len),
> +
> +	    TP_ARGS(desc, text, len),
> +
> +	    TP_STRUCT__entry(
> +			__field(const struct _ddebug *, desc)
> +			__dynamic_array(char, msg, len + 1)
> +		    ),
> +
> +	    TP_fast_assign(
> +			__entry->desc = desc;
> +			/*
> +			 * Each trace entry is printed in a new line.
> +			 * If the msg finishes with '\n', cut it off
> +			 * to avoid blank lines in the trace.
> +			 */
> +			if (len > 0 && (text[len - 1] == '\n'))
> +				len -= 1;
> +
> +			memcpy(__get_str(msg), text, len);
> +			__get_str(msg)[len] = 0;
> +		    ),
> +


> +	    TP_printk("%s.%s %s", __entry->desc->modname,
> +		      __entry->desc->function, __get_str(msg))
> +);
> +

That TP_printk() is dangerous. How do you know __entry->desc still exists
when reading the buffer?

Is the struct _ddebug permanent? Can it be freed? If so, the above can
easily cause a crash.

-- Steve