linux-kernel - Re: squashfs: Avoid mem leak in squashfs_fill

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Message-ID: <aJsHZmHN2I712xX3@stanley.mountain>
Date: Tue, 12 Aug 2025 12:20:38 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Markus Elfring <Markus.Elfring@....de>
Cc: Scott Guo <scott_gzh@....com>,
	Phillip Lougher <phillip@...ashfs.org.uk>,
	Scott Guo <scottzhguo@...cent.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org
Subject: Re: squashfs: Avoid mem leak in squashfs_fill_super

On Tue, Aug 12, 2025 at 10:38:59AM +0200, Markus Elfring wrote:
> > Please, don't introduce more of those e_inval, e_nomem labels.
> 
> Would you find any other label identifiers more helpful for sharing
> error code assignments according to better exception handling?

Just assign "err = -EINVAL" before the goto everyone else does.

The common kernel error handling style is called an "unwind ladder".
Assigning the error code is not part of the unwind process and it
messes up the top rung of the unwind ladder.

//=================== Good =============================
	return 0;

err_free_thing:
	free(thing);
	return ret;

//=================== Bad ==============================
	return 0;

e_inval:
        ret = -EINVAL;
        free(something);
        return ret;

Now imagine you need to add a new free:

//=================== Good =============================
	return 0;

err_free_other_thing:
	free(other_thing);
err_free_thing:
	free(thing);
	return ret;

//=================== Bad ==============================
	return 0;

e_inval:
	ret = -EINVAL;
	goto fail;
free_other_thing:
	free(other_thing);
fail:
	free(something);
	return ret;

Also, in places which basically hardcode -EINVAL into of the unwind, then
it's pretty common for later updates to carry on returning -EINVAL even
when it's the wrong error code.

regards,
dan carpenter