[PATCH v2] ARM: xen: validate hypervisor compatible before parsing its version

[Pengpeng Hou]

fdt_find_hyper_node() reads the raw compatible property and then derives
hyper_node.version from a prefix match before later printing it with %s.
Flat DT properties are external boot input, and this path does not prove
that the first compatible entry is NUL-terminated within the returned
property length.

Keep the existing flat-DT lookup path, but verify that the first
compatible entry terminates within the returned property length before
deriving the version suffix from it.

Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
Changes since v1:
- keep `of_get_flat_dt_prop()` instead of switching to `fdt_stringlist_get()`
- validate the first compatible entry with bounded `strnlen()`

 arch/arm/xen/enlighten.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 4feed2c2..25a0ce3b 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -218,8 +218,9 @@ static __initdata struct {
 static int __init fdt_find_hyper_node(unsigned long node, const char *uname,
 				      int depth, void *data)
 {
-	const void *s = NULL;
+	const char *s = NULL;
 	int len;
+	size_t prefix_len = strlen(hyper_node.prefix);
 
 	if (depth != 1 || strcmp(uname, "hypervisor") != 0)
 		return 0;
@@ -228,9 +229,10 @@ static int __init fdt_find_hyper_node(unsigned long node, const char *uname,
 		hyper_node.found = true;
 
 	s = of_get_flat_dt_prop(node, "compatible", &len);
-	if (strlen(hyper_node.prefix) + 3  < len &&
-	    !strncmp(hyper_node.prefix, s, strlen(hyper_node.prefix)))
-		hyper_node.version = s + strlen(hyper_node.prefix);
+	if (s && len > 0 && strnlen(s, len) < len &&
+	    len > prefix_len + 3 &&
+	    !strncmp(hyper_node.prefix, s, prefix_len))
+		hyper_node.version = s + prefix_len;
 
 	/*
 	 * Check if Xen supports EFI by checking whether there is the
-- 
2.50.1