linux-ext4 - Re: [PATCH] ext4: avoid utf8_strncasecmp() with unstable name

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Date:   Sat, 30 May 2020 10:18:14 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, stable@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Daniel Rosenberg <drosen@...gle.com>,
        Gabriel Krisman Bertazi <krisman@...labora.co.uk>
Subject: Re: [PATCH] ext4: avoid utf8_strncasecmp() with unstable name

On Fri, May 29, 2020 at 11:02:16PM -0700, Eric Biggers wrote:
> +	if (len <= DNAME_INLINE_LEN - 1) {
> +		unsigned int i;
> +
> +		for (i = 0; i < len; i++)
> +			strbuf[i] = READ_ONCE(str[i]);
> +		strbuf[len] = 0;

This READ_ONCE is going to force the compiler to use byte accesses.
What's wrong with using a plain memcpy()?

> +		qstr.name = strbuf;
> +	}
> +
>  	return ext4_ci_compare(inode, name, &qstr, false);
>  }
>  
> -- 
> 2.26.2
>