linux-kernel - Re: [PATCH] module: Fix use-after-free bug in read_file_mod

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Date:   Wed, 17 May 2023 12:03:39 +0530
From:   Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To:     mcgrof@...nel.org, linux-modules@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, error27@...il.com,
        kernel-janitors@...r.kernel.org, arnd@...db.de,
        dan.carpenter@...aro.org
Subject: Re: [PATCH] module: Fix use-after-free bug in read_file_mod_stats()

Hi,
On 28/04/23 11:29 am, Harshit Mogalapalli wrote:
> Smatch warns:
> 	kernel/module/stats.c:394 read_file_mod_stats()
> 	warn: passing freed memory 'buf'
> 
> We are passing 'buf' to simple_read_from_buffer() after freeing it.
> 
> Fix this by changing the order of 'simple_read_from_buffer' and 'kfree'.
> 

Friendly reminder to review this patch.

Thanks,
Harshit


> Fixes: df3e764d8e5c ("module: add debug stats to help identify memory pressure")
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
> ---
> Found with statis analysis, only compile tested.
> ---
>   kernel/module/stats.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/module/stats.c b/kernel/module/stats.c
> index ad7b6ada29f2..6ab2c94d6bc3 100644
> --- a/kernel/module/stats.c
> +++ b/kernel/module/stats.c
> @@ -276,6 +276,7 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
>   	struct mod_fail_load *mod_fail;
>   	unsigned int len, size, count_failed = 0;
>   	char *buf;
> +	int ret;
>   	u32 live_mod_count, fkreads, fdecompress, fbecoming, floads;
>   	unsigned long total_size, text_size, ikread_bytes, ibecoming_bytes,
>   		idecompress_bytes, imod_bytes, total_virtual_lost;
> @@ -390,8 +391,9 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
>   out_unlock:
>   	mutex_unlock(&module_mutex);
>   out:
> +	ret = simple_read_from_buffer(user_buf, count, ppos, buf, len);
>   	kfree(buf);
> -        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
> +	return ret;
>   }
>   #undef MAX_PREAMBLE
>   #undef MAX_FAILED_MOD_PRINT