[PATCH 7/8] libfdt: Check for multiple/invalid root nodes

[Simon Glass]

It is possible to construct a devicetree blob with multiple root nodes.
Update fdt_check_full() to check for this, along with a root node with an
invalid name.

CVE-2021-27097

Signed-off-by: Simon Glass <sjg at chromium.org>
Reported-by: Bruce Monroe <bruce.monroe at intel.com>
Reported-by: Arie Haenel <arie.haenel at intel.com>
Reported-by: Julien Lenoir <julien.lenoir at intel.com>
---

 scripts/dtc/libfdt/fdt_ro.c | 17 +++++++++++++++++
 test/py/tests/test_vboot.py |  3 ++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/scripts/dtc/libfdt/fdt_ro.c b/scripts/dtc/libfdt/fdt_ro.c
index d984bab036b..efe7efe9211 100644
--- a/scripts/dtc/libfdt/fdt_ro.c
+++ b/scripts/dtc/libfdt/fdt_ro.c
@@ -867,6 +867,7 @@ int fdt_check_full(const void *fdt, size_t bufsize)
 	unsigned depth = 0;
 	const void *prop;
 	const char *propname;
+	bool expect_end = false;
 
 	if (bufsize < FDT_V1_SIZE)
 		return -FDT_ERR_TRUNCATED;
@@ -887,6 +888,10 @@ int fdt_check_full(const void *fdt, size_t bufsize)
 		if (nextoffset < 0)
 			return nextoffset;
 
+		/* If we see two root nodes, something is wrong */
+		if (expect_end && tag != FDT_END)
+			return -FDT_ERR_BADLAYOUT;
+
 		switch (tag) {
 		case FDT_NOP:
 			break;
@@ -900,12 +905,24 @@ int fdt_check_full(const void *fdt, size_t bufsize)
 			depth++;
 			if (depth > INT_MAX)
 				return -FDT_ERR_BADSTRUCTURE;
+
+			/* The root node must have an empty name */
+			if (depth == 1) {
+				const char *name;
+				int len;
+
+				name = fdt_get_name(fdt, offset, &len);
+				if (*name || len)
+					return -FDT_ERR_BADLAYOUT;
+			}
 			break;
 
 		case FDT_END_NODE:
 			if (depth == 0)
 				return -FDT_ERR_BADSTRUCTURE;
 			depth--;
+			if (depth == 0)
+				expect_end = true;
 			break;
 
 		case FDT_PROP:
diff --git a/test/py/tests/test_vboot.py b/test/py/tests/test_vboot.py
index 9cdc290b9fc..22e8fc10d83 100644
--- a/test/py/tests/test_vboot.py
+++ b/test/py/tests/test_vboot.py
@@ -255,7 +255,8 @@ def test_vboot(u_boot_console, sha_algo, padding, sign_options, required,
             util.run_and_log_expect_exception(
                 cons, [fit_check_sign, '-f', efit, '-k', dtb],
                 1, 'Failed to verify required signature')
-            run_bootm(sha_algo, 'evil fakeroot', 'Bad Data Hash', False, efit)
+            run_bootm(sha_algo, 'evil fakeroot', 'Bad FIT kernel image format',
+                      False, efit)
 
             # Try adding an @ to the kernel node name. This should be detected.
             efit = '%stest.evilk.fit' % tmpdir
-- 
2.30.0.478.g8a0d178c01-goog