From 761c1745f977e593600facdd0864e7e88fcc1c16 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 4 Aug 2025 08:40:27 -0700
Subject: iommu/amd: Avoid stack buffer overflow from kernel cmdline

From: Kees Cook <kees@kernel.org>

[ Upstream commit 8503d0fcb1086a7cfe26df67ca4bd9bd9e99bdec ]

While the kernel command line is considered trusted in most environments,
avoid writing 1 byte past the end of "acpiid" if the "str" argument is
maximum length.

Reported-by: Simcha Kosman <simcha.kosman@cyberark.com>
Closes: https://lore.kernel.org/all/AS8P193MB2271C4B24BCEDA31830F37AE84A52@AS8P193MB2271.EURP193.PROD.OUTLOOK.COM
Fixes: b6b26d86c61c ("iommu/amd: Add a length limitation for the ivrs_acpihid command-line parameter")
Signed-off-by: Kees Cook <kees@kernel.org>
Reviewed-by: Ankit Soni <Ankit.Soni@amd.com>
Link: https://lore.kernel.org/r/20250804154023.work.970-kees@kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iommu/amd/init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 2e7a12f30651..431cea41df2a 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3625,7 +3625,7 @@ static int __init parse_ivrs_acpihid(char *str)
 {
 	u32 seg = 0, bus, dev, fn;
 	char *hid, *uid, *p, *addr;
-	char acpiid[ACPIID_LEN] = {0};
+	char acpiid[ACPIID_LEN + 1] = { }; /* size with NULL terminator */
 	int i;
 
 	addr = strchr(str, '@');
@@ -3651,7 +3651,7 @@ static int __init parse_ivrs_acpihid(char *str)
 	/* We have the '@', make it the terminator to get just the acpiid */
 	*addr++ = 0;
 
-	if (strlen(str) > ACPIID_LEN + 1)
+	if (strlen(str) > ACPIID_LEN)
 		goto not_found;
 
 	if (sscanf(str, "=%s", acpiid) != 1)
-- 
2.50.1