linux-ext4 - Re: [PATCH v2 05/12] ss_create_invocation: fix memory leak and check whether NULL pointer

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Date:   Thu, 15 Jul 2021 23:34:57 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     wuguanghao <wuguanghao3@...wei.com>
Cc:     linux-ext4@...r.kernel.org, artem.blagodarenko@...il.com,
        liuzhiqiang26@...wei.com, linfeilong@...wei.com
Subject: Re: [PATCH v2 05/12] ss_create_invocation: fix memory leak and check
 whether NULL pointer

On Wed, Jun 30, 2021 at 04:27:17PM +0800, wuguanghao wrote:
> In ss_create_invocation(), it is necessary to check whether
> returned by malloc is a null pointer.
> 
> Signed-off-by: Wu Guanghao <wuguanghao3@...wei.com>
> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
> ---
>  lib/ss/invocation.c | 38 ++++++++++++++++++++++++++++++++------
>  1 file changed, 32 insertions(+), 6 deletions(-)
> 

Instead of adding all of these goto targets (which is fragile if for
some reason the code gets rearranged), it would be better to make sure
everything that we might want to free is initialized, i.e.:

  	register ss_data *new_table = NULL;
  	register ss_data **table = NULL;

  	new_table = (ss_data *) malloc(sizeof(ss_data));
	if (!new_table)
		goto out;
	memset(new_table, 0, sizeof(ss_data));

and then exit path can just look like this:

out:
	if (new_table) {
		free(new_table->prompt);
		free(new_table->info_dirs);
	}
	free(new_table);
	free(table);
	*code_ptr = ENOMEM;
	return 0;

... which is much cleaner, and means in the future, you don't need to
figure out which goto label you might need to jump to.

Cheers,

					- Ted

P.S.  And if we are making all of these changes to the function's
initializers, it might be a good time to zap the "register" keywords
for any lines we are changing, or are nearby, while we're at it.