linux-kernel - Re: [PATCH v3 18/19] firmware: Add request_partial_firmware_into

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Message-ID: <202007291042.D43AA4AB37@keescook>
Date:   Wed, 29 Jul 2020 10:43:39 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Scott Branden <scott.branden@...adcom.com>,
        Mimi Zohar <zohar@...ux.ibm.com>, Jessica Yu <jeyu@...nel.org>,
        SeongJae Park <sjpark@...zon.de>,
        KP Singh <kpsingh@...omium.org>, linux-efi@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 18/19] firmware: Add
 request_partial_firmware_into_buf()

On Wed, Jul 29, 2020 at 08:22:17AM +0200, Takashi Iwai wrote:
> On Wed, 29 Jul 2020 03:17:39 +0200,
> Luis Chamberlain wrote:
> > 
> > Long ago Takashi had some points about this strategy breaking
> > compressed file use. Was that considered?
> 
> As long as I read the patch, it tries to skip both the compressed and
> the fallback loading when FW_OPT_PARTIAL is set, which is good.
> 
> However...
> 
> > > @@ -771,18 +805,20 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
> > >  	}
> > >  
> > >  	ret = _request_firmware_prepare(&fw, name, device, buf, size,
> > > -					opt_flags);
> > > +					offset, opt_flags);
> > >  	if (ret <= 0) /* error or already assigned */
> > >  		goto out;
> > >  
> > >  	ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL);
> > > -#ifdef CONFIG_FW_LOADER_COMPRESS
> > > -	if (ret == -ENOENT)
> > > +
> > > +	/* Only full reads can support decompression, platform, and sysfs. */
> > > +	if (!(opt_flags & FW_OPT_PARTIAL))
> > > +		nondirect = true;
> > > +
> > > +	if (ret == -ENOENT && nondirect)
> > >  		ret = fw_get_filesystem_firmware(device, fw->priv, ".xz",
> > >  						 fw_decompress_xz);
> > > -#endif
> 
> ... by dropping this ifdef, the fw loader would try to access *.xz
> file unnecessarily even if CONFIG_FW_LOADER_COMPRESS is disabled.

Ah, good point. I'd added the -ENOENT fw_decompress_xz, but I take your
point about the needless access. I will switch this back to an #ifdef.

-- 
Kees Cook