linux-kernel - Re: [PATCH] trace: Avoid memory leak in predicate

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Date:   Tue, 28 May 2019 22:48:46 +0200
From:   Tomas Bortoli <tomasbortoli@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com
Subject: Re: [PATCH] trace: Avoid memory leak in predicate_parse()

On 5/28/19 10:31 PM, Steven Rostedt wrote:
> On Tue, 28 May 2019 17:43:38 +0200
> Tomas Bortoli <tomasbortoli@...il.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@...il.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@...r.kernel.org
> Fixes: 80765597bc587 ("tracing: Rewrite filter logic to be simpler and faster")
> Reported-by: syzbot+6b8e0fb820e570c59e19@...kaller.appspotmail.com
> Signed-off-by: Tomas Bortoli <tomasbortoli@...il.com>
> [ Added protection around freeing prog_stack[i].pred ]
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.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);
>  }
>  
> 

Oops again, I should have been more careful.

Thanks.