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Date: Mon, 14 Oct 2024 17:54:27 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Kees Cook <kees@kernel.org>
Cc: Justin Stitt <justinstitt@google.com>, Masami Hiramatsu
 <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
 linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2] tracing: replace multiple deprecated strncpy with
 memcpy
Message-ID: <20241014175427.4bcf9020@gandalf.local.home>
In-Reply-To: <202410141423.2C30F35EE0@keescook>
References: <20241014-strncpy-kernel-trace-trace_events_filter-c-v2-1-d821e81e371e@google.com>
	<202410141423.2C30F35EE0@keescook>
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On Mon, 14 Oct 2024 14:31:29 -0700
Kees Cook <kees@kernel.org> wrote:
> 
> We know the destination must have a NUL-terminated string. Is the src
> NUL terminated? Looking at parse_pred(), it seems like no? And we can't
> use memtostr_pad() here because the source buffer size isn't known at
> compile time. Okay then. And there are no NUL bytes in the "str + s"
> span, so yeah, it looks like memcpy() is best.
> 
> Reviewed-by: Kees Cook <kees@kernel.org>
> 

The code is simply breaking up parts of one string and copying the bits
into other strings. Like the example that broke:

$ echo 'common_pid != 0 && common_pid != 120 && common_pid != 1253 &&
  common_pid != 17 && common_pid != 394 && common_pid != 81 &&
  common_pid != 87' > /sys/kernel/tracing/events/sched/sched_switch/filter

It would need to move each of the above tokens "common_pid", "!=", "0", "&&", etc
into their own strings for later processing. The parser finds the start and
end of the location needed to copy, so memcpy() followed by a nul byte is fine.

-- Steve