[PATCH 1/2] of: address: Fix empty resource handling in __of_address_resource_bounds()

["Thomas Weißschuh" <thomas.weissschuh@linutronix.de>]

"resource->end" needs to always be equal to "resource->start + size - 1".
The previous version of the function did not perform the "- 1" in case
of an empty resource.

Also make sure to allow an empty resource at address 0.

Reported-by: Basharath Hussain Khaja <basharath@couthit.com>
Closes: https://lore.kernel.org/lkml/20250108140414.13530-1-basharath@couthit.com/
Fixes: 1a52a094c2f0 ("of: address: Unify resource bounds overflow checking")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 drivers/of/address.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/of/address.c b/drivers/of/address.c
index 8770004d9b085f1ff40f693d695d284a6ef3dfde..5c0663066a7f3816a05077f99124ca25e3c152d7 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -200,17 +200,15 @@ static u64 of_bus_pci_map(__be32 *addr, const __be32 *range, int na, int ns,
 
 static int __of_address_resource_bounds(struct resource *r, u64 start, u64 size)
 {
-	u64 end = start;
-
 	if (overflows_type(start, r->start))
 		return -EOVERFLOW;
-	if (size && check_add_overflow(end, size - 1, &end))
-		return -EOVERFLOW;
-	if (overflows_type(end, r->end))
-		return -EOVERFLOW;
 
 	r->start = start;
-	r->end = end;
+
+	if (!size)
+		r->end = wrapping_sub(typeof(r->end), r->start, 1);
+	else if (size && check_add_overflow(r->start, size - 1, &r->end))
+		return -EOVERFLOW;
 
 	return 0;
 }

-- 
2.48.1