linux-kernel - Re: [PATCH] ftrace: Check if pages were allocated before calling free

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Date:   Tue, 6 Apr 2021 08:27:26 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: Check if pages were allocated before calling
 free_pages()

On Tue,  6 Apr 2021 14:51:45 +0800
Jiapeng Chong <jiapeng.chong@...ux.alibaba.com> wrote:

> It is possible that on error pg->size can be zero when getting its
> order,which would return a -1 value. It is dangerous to pass in an
> order of -1 to free_pages(). Check if order is greater than or equal
> to zero before calling free_pages().
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> ---
>  kernel/trace/ftrace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index b7e29db..74efc33 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6811,7 +6811,8 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr)
>  		if (!pg->index) {
>  			*last_pg = pg->next;
>  			order = get_count_order(pg->size / ENTRIES_PER_PAGE);
> -			free_pages((unsigned long)pg->records, order);
> +			if (order >= 0)
> +				free_pages((unsigned long)pg->records, order);

This has already been fixed upstream.

-- Steve

>  			ftrace_number_of_pages -= 1 << order;
>  			ftrace_number_of_groups--;
>  			kfree(pg);