linux-kernel - Re: [PATCH] unicode: mkutf8data: Add malloc return value detection

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Date:   Fri, 14 Oct 2022 14:03:34 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Li zeming <zeming@...china.com>
Cc:     krisman@...labora.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] unicode: mkutf8data: Add malloc return value detection

On Fri, Oct 14, 2022 at 03:57:10PM +0800, Li zeming wrote:
> Add the check and judgment statement of malloc return value.

Why?  Just to shut up some static checker?

> +++ b/fs/unicode/mkutf8data.c
> @@ -495,6 +495,9 @@ static struct node *alloc_node(struct node *parent)
>  	int bitnum;
>  
>  	node = malloc(sizeof(*node));
> +	if (unlikely(!node))
> +		return NULL;
> +

Right, so now alloc_node() can return NULL when it couldn't before.
Look at the callers ...

        while (keybits) {
                if (!*cursor)
                        *cursor = alloc_node(node);
                node = *cursor;
                if (node->nextbyte)
                        key++;

They're unprepared for alloc_node() to return NULL, so all you've done
is move the crash.