iommu/amd: Add a length limitation for the ivrs_acpihid command-line parameter

The 'acpiid' buffer in the parse_ivrs_acpihid function may overflow,
because the string specifier in the format string sscanf()
has no width limitation.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.

Fixes: ca3bf5d ("iommu/amd: Introduces ivrs_acpihid kernel parameter")
Cc: stable@vger.kernel.org
Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@infotecs.ru>
Reviewed-by: Kim Phillips <kim.phillips@amd.com>
Link: https://lore.kernel.org/r/20230202082719.1513849-1-Ilia.Gavrilov@infotecs.ru
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: Gavrilov Ilia

drivers/iommu/amd/init.c

@@ -3475,15 +3475,26 @@ static int __init parse_ivrs_hpet(char *str)
 	return 1;
 }
 
+#define ACPIID_LEN (ACPIHID_UID_LEN + ACPIHID_HID_LEN)
+
 static int __init parse_ivrs_acpihid(char *str)
 {
 	u32 seg = 0, bus, dev, fn;
 	char *hid, *uid, *p, *addr;
-	char acpiid[ACPIHID_UID_LEN + ACPIHID_HID_LEN] = {0};
+	char acpiid[ACPIID_LEN] = {0};
 	int i;
 
 	addr = strchr(str, '@');
 	if (!addr) {
+		addr = strchr(str, '=');
+		if (!addr)
+			goto not_found;
+
+		++addr;
+
+		if (strlen(addr) > ACPIID_LEN)
+			goto not_found;
+
 		if (sscanf(str, "[%x:%x.%x]=%s", &bus, &dev, &fn, acpiid) == 4 ||
 		    sscanf(str, "[%x:%x:%x.%x]=%s", &seg, &bus, &dev, &fn, acpiid) == 5) {
 			pr_warn("ivrs_acpihid%s option format deprecated; use ivrs_acpihid=%s@%04x:%02x:%02x.%d instead\n",
@@ -3496,6 +3507,9 @@ 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)
+		goto not_found;
+
 	if (sscanf(str, "=%s", acpiid) != 1)
 		goto not_found;