[PATCH] libfdt: Validate alias property value is a valid string.

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Prevent circular alias resolution causing infinite recursion.

Signed-off-by: Mike McTernan <mikemcternan@xxxxxxxxxx>
---
 libfdt/fdt_ro.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index 9f6c551..870c4a5 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -525,13 +525,27 @@ uint32_t fdt_get_phandle(const void *fdt, int nodeoffset)
 const char *fdt_get_alias_namelen(const void *fdt,
 				  const char *name, int namelen)
 {
+	const char *prop;
 	int aliasoffset;
+	int prop_len;
 
 	aliasoffset = fdt_path_offset(fdt, "/aliases");
 	if (aliasoffset < 0)
 		return NULL;
 
-	return fdt_getprop_namelen(fdt, aliasoffset, name, namelen, NULL);
+	prop = fdt_getprop_namelen(fdt, aliasoffset, name, namelen, &prop_len);
+	if (prop && !can_assume(VALID_INPUT)) {
+		/* Validate the alias value.  From the devicetree spec v0.3:
+		 * "An alias value is a device path and is encoded as a string.
+		 *  The value representes the full path to a node, ..."
+		 * A full path must start at the root to prevent recursion.
+		 */
+		if (prop_len < 2 || *prop != '/' || strnlen(prop, prop_len) != prop_len - 1) {
+			prop = NULL;
+		}
+	}
+
+	return prop;
 }
 
 const char *fdt_get_alias(const void *fdt, const char *name)
-- 
2.38.0.rc2.412.g84df46c1b4-goog




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