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Date:   Mon, 24 Apr 2023 16:06:46 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Hao Zeng <zenghao@kylinos.cn>
Cc:     chenhuacai@kernel.org, zhangqing@loongson.cn,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] recordmcount: Fix memory leaks in the uwrite function
Message-ID: <20230424160646.3faf00f1@rorschach.local.home>
In-Reply-To: <20230412093048.3005276-1-zenghao@kylinos.cn>
References: <20230412093048.3005276-1-zenghao@kylinos.cn>
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On Wed, 12 Apr 2023 17:30:48 +0800
Hao Zeng <zenghao@kylinos.cn> wrote:

> Common realloc mistake: 'file_append' nulled but not freed upon failure
> 
> Signed-off-by: Hao Zeng <zenghao@kylinos.cn>
> ---
>  scripts/recordmcount.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> index e30216525325..2b7173a86d4c 100644
> --- a/scripts/recordmcount.c
> +++ b/scripts/recordmcount.c
> @@ -110,22 +110,23 @@ static ssize_t uwrite(void const *const buf, size_t const count)
>  {
>  	size_t cnt = count;
>  	off_t idx = 0;
> -
> +	void *p = NULL;
>  	file_updated = 1;
>  
>  	if (file_ptr + count >= file_end) {
>  		off_t aoffset = (file_ptr + count) - file_end;
>  
>  		if (aoffset > file_append_size) {
> -			file_append = realloc(file_append, aoffset);
> +			p = realloc(file_append, aoffset);
> +			if (!p) {
> +				perror("write");
> +				file_append_cleanup();
> +				mmap_cleanup();
> +				return -1;
> +			}
> +			file_append = p;
>  			file_append_size = aoffset;
>  		}

This changes the logic of the function. If file_append is NULL when
entering, and does not get into the allocate path we still want this to
error.

Just do:

		p = realloc(file_append, aoffset);
		if (!p) {
			free(file_append);
			file_append = NULL;
		}

And that keeps the same logic but removes the memory leak.

-- Steve


> -		if (!file_append) {
> -			perror("write");
> -			file_append_cleanup();
> -			mmap_cleanup();
> -			return -1;
> -		}
>  		if (file_ptr < file_end) {
>  			cnt = file_end - file_ptr;
>  		} else {