[PATCH 29/32] xtensa: Use mem_to_flex_dup() with struct property

[Kees Cook]

As part of the work to perform bounds checking on all memcpy() uses,
replace the open-coded a deserialization of bytes out of memory into a
trailing flexible array by using a flex_array.h helper to perform the
allocation, bounds checking, and copying.

Cc: Chris Zankel <chris at zankel.net>
Cc: Max Filippov <jcmvbkbc at gmail.com>
Cc: Rob Herring <robh+dt at kernel.org>
Cc: Frank Rowand <frowand.list at gmail.com>
Cc: Guenter Roeck <linux at roeck-us.net>
Cc: linux-xtensa at linux-xtensa.org
Cc: devicetree at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 arch/xtensa/platforms/xtfpga/setup.c | 9 +++------
 include/linux/of.h                   | 3 ++-
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/xtensa/platforms/xtfpga/setup.c b/arch/xtensa/platforms/xtfpga/setup.c
index 538e6748e85a..31c1fa4ba4ec 100644
--- a/arch/xtensa/platforms/xtfpga/setup.c
+++ b/arch/xtensa/platforms/xtfpga/setup.c
@@ -102,7 +102,7 @@ CLK_OF_DECLARE(xtfpga_clk, "cdns,xtfpga-clock", xtfpga_clk_setup);
 #define MAC_LEN 6
 static void __init update_local_mac(struct device_node *node)
 {
-	struct property *newmac;
+	struct property *newmac = NULL;
 	const u8* macaddr;
 	int prop_len;
 
@@ -110,19 +110,16 @@ static void __init update_local_mac(struct device_node *node)
 	if (macaddr == NULL || prop_len != MAC_LEN)
 		return;
 
-	newmac = kzalloc(sizeof(*newmac) + MAC_LEN, GFP_KERNEL);
-	if (newmac == NULL)
+	if (mem_to_flex_dup(&newmac, macaddr, MAC_LEN, GFP_KERNEL))
 		return;
 
-	newmac->value = newmac + 1;
-	newmac->length = MAC_LEN;
+	newmac->value = newmac->contents;
 	newmac->name = kstrdup("local-mac-address", GFP_KERNEL);
 	if (newmac->name == NULL) {
 		kfree(newmac);
 		return;
 	}
 
-	memcpy(newmac->value, macaddr, MAC_LEN);
 	((u8*)newmac->value)[5] = (*(u32*)DIP_SWITCHES_VADDR) & 0x3f;
 	of_update_property(node, newmac);
 }
diff --git a/include/linux/of.h b/include/linux/of.h
index 17741eee0ca4..efb0f419fd1f 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -30,7 +30,7 @@ typedef u32 ihandle;
 
 struct property {
 	char	*name;
-	int	length;
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(int, length);
 	void	*value;
 	struct property *next;
 #if defined(CONFIG_OF_DYNAMIC) || defined(CONFIG_SPARC)
@@ -42,6 +42,7 @@ struct property {
 #if defined(CONFIG_OF_KOBJ)
 	struct bin_attribute attr;
 #endif
+	DECLARE_FLEX_ARRAY_ELEMENTS(u8, contents);
 };
 
 #if defined(CONFIG_SPARC)
-- 
2.32.0