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

[Pengpeng Hou <pengpeng@xxxxxxxxxxx>]

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 compatible string is NUL-terminated within its
declared bounds.

Fetch the first compatible entry with fdt_stringlist_get() so malformed
unterminated properties are rejected before the version suffix is
parsed.

Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
 arch/arm/xen/enlighten.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 4feed2c2498d..f69290a4c639 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -19,6 +19,7 @@
 #include <asm/efi.h>
 #include <linux/interrupt.h>
 #include <linux/irqreturn.h>
+#include <linux/libfdt.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_fdt.h>
@@ -218,8 +219,9 @@ 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;
@@ -227,10 +229,10 @@ static int __init fdt_find_hyper_node(unsigned long node, 
const char *uname,
        if (of_flat_dt_is_compatible(node, hyper_node.compat))
                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);
+       s = fdt_stringlist_get(initial_boot_params, node, "compatible", 0, 
&len);
+       if (s && len > prefix_len + 2 &&
+           !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 (Apple Git-155)