[PATCH v3 18/19] firmware: Add request_partial_firmware_into_buf()

[Kees Cook]

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