linux-kernel - Re: Potential out-of-bounds in ftrace_regex

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Date:	Wed, 9 Oct 2013 22:23:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrey Konovalov <andreyknvl@...gle.com>
Cc:	Dave Jones <davej@...hat.com>, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, mingo@...hat.com,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>
Subject: Re: Potential out-of-bounds in ftrace_regex_release

On Wed, 9 Oct 2013 14:05:26 +0400
Andrey Konovalov <andreyknvl@...gle.com> wrote:

> So I still think that the bug is in 'trage_get_user()':
> Checking that 'parser->idx < parser->size - 1' is not performed in 'if
> (isspace(ch))' section, so 'parser->idx' becomes equal to
> 'parser->size' after 'parser->buffer[parser->idx++] = ch;'.
> (However in 'while (cnt && !isspace(ch))' loop checking is performed.)

Yep, you are correct. I put in some printk's and did same writing to
the set_events file and was able to prove that I could get that "0"
written into the +1 overflow boundary.

Can you try this patch to see if it fixes it for you.

Thanks,

-- Steve

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d5f7c4d..063a92b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -843,9 +843,12 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 	if (isspace(ch)) {
 		parser->buffer[parser->idx] = 0;
 		parser->cont = false;
-	} else {
+	} else if (parser->idx < parser->size - 1) {
 		parser->cont = true;
 		parser->buffer[parser->idx++] = ch;
+	} else {
+		ret = -EINVAL;
+		goto out;
 	}
 
 	*ppos += read;

--
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