linux-hardening - Re: [PATCH] firmware: coreboot: Check size of table entry and split memcpy

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Date:   Fri, 6 Jan 2023 12:34:52 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Julius Werner <jwerner@...omium.org>
Cc:     Jack Rosenthal <jrosenth@...omium.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        Guenter Roeck <groeck@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] firmware: coreboot: Check size of table entry and split
 memcpy

On Fri, Jan 06, 2023 at 04:03:35PM +0100, Julius Werner wrote:
> Have you considered adding the flexible array member directly to the
> union in struct coreboot_device instead? I think that would make this
> a bit simpler by not having to copy header and data portion
> separately.

Are you thinking something like this?


diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
index 2652c396c423..564a3c908838 100644
--- a/drivers/firmware/google/coreboot_table.c
+++ b/drivers/firmware/google/coreboot_table.c
@@ -93,14 +93,19 @@ static int coreboot_table_populate(struct device *dev, void *ptr)
 	for (i = 0; i < header->table_entries; i++) {
 		entry = ptr_entry;
 
-		device = kzalloc(sizeof(struct device) + entry->size, GFP_KERNEL);
+		if (entry->size < sizeof(*entry)) {
+			dev_warn(dev, "coreboot table entry too small!\n");
+			return -EINVAL;
+		}
+
+		device = kzalloc(sizeof(device->dev) + entry->size, GFP_KERNEL);
 		if (!device)
 			return -ENOMEM;
 
 		device->dev.parent = dev;
 		device->dev.bus = &coreboot_bus_type;
 		device->dev.release = coreboot_device_release;
-		memcpy(&device->entry, ptr_entry, entry->size);
+		memcpy(device->raw, entry, entry->size);
 
 		switch (device->entry.tag) {
 		case LB_TAG_CBMEM_ENTRY:
diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index 37f4d335a606..d814dca33a08 100644
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -79,6 +79,7 @@ struct coreboot_device {
 		struct lb_cbmem_ref cbmem_ref;
 		struct lb_cbmem_entry cbmem_entry;
 		struct lb_framebuffer framebuffer;
+		DECLARE_FLEX_ARRAY(u8, raw);
 	};
 };
 

-- 
Kees Cook