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Date: Sun, 3 Mar 2024 08:02:12 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Masami Hiramatsu
 <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Sachin Sant <sachinp@linux.ibm.com>
Subject: Re: [GIT PULL] tracing: Prevent trace_marker being bigger than
 unsigned short
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On Sun, 3 Mar 2024 07:59:37 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> >   
> 
> I believe I was trying to solve this wrong. The vsprintf() is called on
> reading of the ring buffer, and I was trying to fix it on the write
> side. I believe that the fix should be on the read side where the
> vsprintf() is called.

I prefer this patch, as I found other ways to add large strings into the
ring buffer that can trigger this issue again. This fixes it at the
location of the bug.

-- Steve


> 
> Sachin, can you try this patch.
> 
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 3e7fa44dc2b2..5c7962d612de 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -1588,11 +1588,20 @@ static enum print_line_t trace_print_print(struct trace_iterator *iter,
>  	struct print_entry *field;
>  	struct trace_seq *s = &iter->seq;
>  	int max = iter->ent_size - offsetof(struct print_entry, buf);
> +	const char *p;
>  
>  	trace_assign_type(field, iter->ent);
>  
>  	seq_print_ip_sym(s, field->ip, flags);
> -	trace_seq_printf(s, ": %.*s", max, field->buf);
> +	trace_seq_puts(s, ": ");
> +	/* Write 1K chunks at a time */
> +	p = field->buf;
> +	do {
> +		int pre = max > 1024 ? 1024 : max;
> +		trace_seq_printf(s, "%.*s", pre, p);
> +		max -= pre;
> +		p += pre;
> +	} while (max > 0);
>  
>  	return trace_handle_return(s);
>  }
> @@ -1602,10 +1611,19 @@ static enum print_line_t trace_print_raw(struct trace_iterator *iter, int flags,
>  {
>  	struct print_entry *field;
>  	int max = iter->ent_size - offsetof(struct print_entry, buf);
> +	const char *p;
>  
>  	trace_assign_type(field, iter->ent);
>  
> -	trace_seq_printf(&iter->seq, "# %lx %.*s", field->ip, max, field->buf);
> +	trace_seq_printf(&iter->seq, "# %lx", field->ip);
> +	/* Write 1K chunks at a time */
> +	p = field->buf;
> +	do {
> +		int pre = max > 1024 ? 1024 : max;
> +		trace_seq_printf(&iter->seq, "%.*s", pre, p);
> +		max -= pre;
> +		p += pre;
> +	} while (max > 0);
>  
>  	return trace_handle_return(&iter->seq);
>  }