Re: [PATCH] trace: Avoid memory leak in predicate_parse()

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 28 May 2019 17:43:38 +0200
Tomas Bortoli <tomasbortoli@gmail.com> wrote:

> @@ -578,6 +578,8 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
>  out_free:
>  	kfree(op_stack);
>  	kfree(inverts);
> +	for (i = 0; prog_stack[i].pred; i++)
> +		kfree(prog_stack[i].pred);
>  	kfree(prog_stack);
>  	return ERR_PTR(ret);
>  }

I should have caught this, but thanks to the zero day bot, it found it
first:

 kernel/trace/trace_events_filter.c:582:27-31: ERROR: prog_stack is NULL but dereferenced.

I changed the patch with the following:

From dfb4a6f2191a80c8b790117d0ff592fd712d3296 Mon Sep 17 00:00:00 2001
From: Tomas Bortoli <tomasbortoli@gmail.com>
Date: Tue, 28 May 2019 17:43:38 +0200
Subject: [PATCH] tracing: Avoid memory leak in predicate_parse()

In case of errors, predicate_parse() goes to the out_free label
to free memory and to return an error code.

However, predicate_parse() does not free the predicates of the
temporary prog_stack array, thence leaking them.

Link: http://lkml.kernel.org/r/20190528154338.29976-1-tomasbortoli@gmail.com

Cc: stable@vger.kernel.org
Fixes: 80765597bc587 ("tracing: Rewrite filter logic to be simpler and faster")
Reported-by: syzbot+6b8e0fb820e570c59e19@syzkaller.appspotmail.com
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
[ Added protection around freeing prog_stack[i].pred ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_events_filter.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index d3e59312ef40..5079d1db3754 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -428,7 +428,7 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 	op_stack = kmalloc_array(nr_parens, sizeof(*op_stack), GFP_KERNEL);
 	if (!op_stack)
 		return ERR_PTR(-ENOMEM);
-	prog_stack = kmalloc_array(nr_preds, sizeof(*prog_stack), GFP_KERNEL);
+	prog_stack = kcalloc(nr_preds, sizeof(*prog_stack), GFP_KERNEL);
 	if (!prog_stack) {
 		parse_error(pe, -ENOMEM, 0);
 		goto out_free;
@@ -579,7 +579,11 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 out_free:
 	kfree(op_stack);
 	kfree(inverts);
-	kfree(prog_stack);
+	if (prog_stack) {
+		for (i = 0; prog_stack[i].pred; i++)
+			kfree(prog_stack[i].pred);
+		kfree(prog_stack);
+	}
 	return ERR_PTR(ret);
 }
 
-- 
2.20.1