[PATCH v2 2/2] efi_loader: efi_net: let efi_net_set_dp properly update the device path

[Tom Rini]

On Sat, Jan 04, 2025 at 12:05:24AM +0100, Heinrich Schuchardt wrote:
> On 06.12.24 18:18, Adriano Cordova wrote:
> > This commit fixes an use after free introduced in Commit e55a4acb54
> > (" efi_loader: net: set EFI bootdevice device path to HTTP when loaded
> > from wget"). The logic in efi_net_set_dp is reworked so that when the
> > function is invoked it not only changes the value of the static variable
> > net_dp (this is how the function was implemented in e55a4acb54) but also
> > updates the protocol interface of the device path protocol in case efi
> > has started.
> > 
> > Fixes: e55a4acb54e8 ("efi_loader: net: set EFI bootdevice device path to HTTP when loaded from wget")
> > Signed-off-by: Adriano Cordova <adriano.cordova at canonical.com>
> > ---
> > Changes in v2: use reinstall_protocol_interface() and new_net_dp in the body of efi_net_set_dp()
> > 
> >   lib/efi_loader/efi_net.c | 61 ++++++++++++++++++++++++++++++++++------
> >   1 file changed, 52 insertions(+), 9 deletions(-)
[snip]
> > @@ -1055,18 +1058,58 @@ out_of_resources:
> >    */
> >   efi_status_t efi_net_set_dp(const char *dev, const char *server)
> >   {
> > -	efi_free_pool(net_dp);
> > +	efi_status_t ret;
> > +	struct efi_handler *phandler;
> > +	struct efi_device_path *old_net_dp, *new_net_dp;
> > 
> > -	net_dp = NULL;
> > +	old_net_dp = net_dp;
> > +	new_net_dp = NULL;
> >   	if (!strcmp(dev, "Net"))
> > -		net_dp = efi_dp_from_eth();
> > +		new_net_dp = efi_dp_from_eth();
> >   	else if (!strcmp(dev, "Http"))
> > -		net_dp = efi_dp_from_http(server);
> > +		new_net_dp = efi_dp_from_http(server);
> > 
> > -	if (!net_dp)
> > +	if (!new_net_dp) {
> >   		return EFI_OUT_OF_RESOURCES;
> > +	}
> > +
> > +	// If netobj is not started yet, end here.
> > +	if (!netobj) {
> > +		goto exit;
> 
> This leads to a build failure with clang as you have not initialized
> variable ret.
> 
> https://source.denx.de/u-boot/custodians/u-boot-efi/-/jobs/987832
> 
> > +	}
> > +
> > +	phandler = NULL;
> > +	efi_search_protocol(&netobj->header, &efi_guid_device_path, &phandler);
> > +
> > +	// If the device path protocol is not yet installed, install it
> > +	if (!phandler)
> > +		goto add;
> > +
> > +	// If it is already installed, try to update it
> > +	ret = efi_reinstall_protocol_interface(&netobj->header, &efi_guid_device_path,
> > +					       old_net_dp, new_net_dp);
> > +	if (ret != EFI_SUCCESS)
> > +		goto error;
> > +
> > +	net_dp = new_net_dp;
> > +	efi_free_pool(old_net_dp);
> > 
> >   	return EFI_SUCCESS;
> > +add:
> > +	ret = efi_add_protocol(&netobj->header, &efi_guid_device_path,
> > +			       new_net_dp);
> > +	if (ret != EFI_SUCCESS)
> > +		goto error;
> > +exit:
> > +	net_dp = new_net_dp;
> 
> Why should we set net_dp if there is no net_obj?

Because prior to this patch we set net_dp = NULL at the start of the
function and with this patch nothing is updating net_dp until much later
in the function.

> Instead of jumping to exit, we can jump to error: with
> 
> ret = EFI_DEVICE_ERROR.

I'm not entirely sure what you mean by that. But can you perhaps v3
this? I still can't re-enable CONFIG_CMD_BOOTEFI_SELFTEST on any of my
platforms due to this problem.

-- 
Tom
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