[PATCH v3 2/2] libfdt: Check that the root-node name is empty

[PATCH v3 2/2] libfdt: Check that the root-node name is empty

[Simon Glass]

The root node is supposed to have an empty name, but at present this is
not checked. The behaviour of such a tree is not well defined. Most
software rightly assumes that the root node is at offset 0 and does not
check the name. This oddity was discovered as part of a security
investigation into U-Boot verified boot.

Add a check for this to fdt_check_full().

Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Reported-by: Arie Haenel <arie.haenel-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Reported-by: Julien Lenoir <julien.lenoir-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---

Changes in v3:
- Add to run_tests.sh also

Changes in v2:
- Use FDT_ERR_BADSTRUCTURE instead of FDT_ERR_BADLAYOUT

 libfdt/fdt_check.c   | 10 ++++++++++
 tests/Makefile.tests |  2 +-
 tests/dumptrees.c    |  3 ++-
 tests/run_tests.sh   |  2 +-
 tests/testdata.h     |  1 +
 tests/trees.S        | 15 +++++++++++++++
 6 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/libfdt/fdt_check.c b/libfdt/fdt_check.c
index 13595a2..fa410a8 100644
--- a/libfdt/fdt_check.c
+++ b/libfdt/fdt_check.c
@@ -59,6 +59,16 @@ 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_BADSTRUCTURE;
+			}
 			break;
 
 		case FDT_END_NODE:
diff --git a/tests/Makefile.tests b/tests/Makefile.tests
index fe5cae8..2b47627 100644
--- a/tests/Makefile.tests
+++ b/tests/Makefile.tests
@@ -33,7 +33,7 @@ LIB_TESTS_L = get_mem_rsv \
 LIB_TESTS = $(LIB_TESTS_L:%=$(TESTS_PREFIX)%)
 
 LIBTREE_TESTS_L = truncated_property truncated_string truncated_memrsv \
-	two_roots
+	two_roots named_root
 
 LIBTREE_TESTS = $(LIBTREE_TESTS_L:%=$(TESTS_PREFIX)%)
 
diff --git a/tests/dumptrees.c b/tests/dumptrees.c
index 02ca092..f1e0ea9 100644
--- a/tests/dumptrees.c
+++ b/tests/dumptrees.c
@@ -24,7 +24,8 @@ static struct {
 	TREE(ovf_size_strings),
 	TREE(truncated_property), TREE(truncated_string),
 	TREE(truncated_memrsv),
-	TREE(two_roots)
+	TREE(two_roots),
+	TREE(named_root)
 };
 
 #define NUM_TREES	(sizeof(trees) / sizeof(trees[0]))
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index 82543fc..5c2b1e8 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -518,7 +518,7 @@ libfdt_tests () {
 	run_test check_full $good
     done
     for bad in truncated_property.dtb truncated_string.dtb \
-		truncated_memrsv.dtb two_roots.dtb; do
+		truncated_memrsv.dtb two_roots.dtb named_root.dtb; do
 	run_test check_full -n $bad
     done
 }
diff --git a/tests/testdata.h b/tests/testdata.h
index d03f352..4f9e3ba 100644
--- a/tests/testdata.h
+++ b/tests/testdata.h
@@ -56,4 +56,5 @@ extern struct fdt_header ovf_size_strings;
 extern struct fdt_header truncated_string;
 extern struct fdt_header truncated_memrsv;
 extern struct fdt_header two_roots;
+extern struct fdt_header named_root;
 #endif /* ! __ASSEMBLY */
diff --git a/tests/trees.S b/tests/trees.S
index e2380b7..95d599d 100644
--- a/tests/trees.S
+++ b/tests/trees.S
@@ -298,3 +298,18 @@ two_roots_strings_end:
 
 two_roots_end:
 
+
+        /* root node with a non-empty name */
+        TREE_HDR(named_root)
+	EMPTY_RSVMAP(named_root)
+
+named_root_struct:
+	BEGIN_NODE("fake")
+	END_NODE
+	FDTLONG(FDT_END)
+named_root_struct_end:
+
+named_root_strings:
+named_root_strings_end:
+
+named_root_end:
-- 
2.31.0.rc2.261.g7f71774620-goog

Re: [PATCH v3 2/2] libfdt: Check that the root-node name is empty

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 4169 bytes --]

On Tue, Mar 23, 2021 at 02:04:10PM +1300, Simon Glass wrote:
> The root node is supposed to have an empty name, but at present this is
> not checked. The behaviour of such a tree is not well defined. Most
> software rightly assumes that the root node is at offset 0 and does not
> check the name. This oddity was discovered as part of a security
> investigation into U-Boot verified boot.
> 
> Add a check for this to fdt_check_full().
> 
> Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> Reported-by: Arie Haenel <arie.haenel-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Reported-by: Julien Lenoir <julien.lenoir-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

Applied, thanks.

> ---
> 
> Changes in v3:
> - Add to run_tests.sh also
> 
> Changes in v2:
> - Use FDT_ERR_BADSTRUCTURE instead of FDT_ERR_BADLAYOUT
> 
>  libfdt/fdt_check.c   | 10 ++++++++++
>  tests/Makefile.tests |  2 +-
>  tests/dumptrees.c    |  3 ++-
>  tests/run_tests.sh   |  2 +-
>  tests/testdata.h     |  1 +
>  tests/trees.S        | 15 +++++++++++++++
>  6 files changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/libfdt/fdt_check.c b/libfdt/fdt_check.c
> index 13595a2..fa410a8 100644
> --- a/libfdt/fdt_check.c
> +++ b/libfdt/fdt_check.c
> @@ -59,6 +59,16 @@ 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_BADSTRUCTURE;
> +			}
>  			break;
>  
>  		case FDT_END_NODE:
> diff --git a/tests/Makefile.tests b/tests/Makefile.tests
> index fe5cae8..2b47627 100644
> --- a/tests/Makefile.tests
> +++ b/tests/Makefile.tests
> @@ -33,7 +33,7 @@ LIB_TESTS_L = get_mem_rsv \
>  LIB_TESTS = $(LIB_TESTS_L:%=$(TESTS_PREFIX)%)
>  
>  LIBTREE_TESTS_L = truncated_property truncated_string truncated_memrsv \
> -	two_roots
> +	two_roots named_root
>  
>  LIBTREE_TESTS = $(LIBTREE_TESTS_L:%=$(TESTS_PREFIX)%)
>  
> diff --git a/tests/dumptrees.c b/tests/dumptrees.c
> index 02ca092..f1e0ea9 100644
> --- a/tests/dumptrees.c
> +++ b/tests/dumptrees.c
> @@ -24,7 +24,8 @@ static struct {
>  	TREE(ovf_size_strings),
>  	TREE(truncated_property), TREE(truncated_string),
>  	TREE(truncated_memrsv),
> -	TREE(two_roots)
> +	TREE(two_roots),
> +	TREE(named_root)
>  };
>  
>  #define NUM_TREES	(sizeof(trees) / sizeof(trees[0]))
> diff --git a/tests/run_tests.sh b/tests/run_tests.sh
> index 82543fc..5c2b1e8 100755
> --- a/tests/run_tests.sh
> +++ b/tests/run_tests.sh
> @@ -518,7 +518,7 @@ libfdt_tests () {
>  	run_test check_full $good
>      done
>      for bad in truncated_property.dtb truncated_string.dtb \
> -		truncated_memrsv.dtb two_roots.dtb; do
> +		truncated_memrsv.dtb two_roots.dtb named_root.dtb; do
>  	run_test check_full -n $bad
>      done
>  }
> diff --git a/tests/testdata.h b/tests/testdata.h
> index d03f352..4f9e3ba 100644
> --- a/tests/testdata.h
> +++ b/tests/testdata.h
> @@ -56,4 +56,5 @@ extern struct fdt_header ovf_size_strings;
>  extern struct fdt_header truncated_string;
>  extern struct fdt_header truncated_memrsv;
>  extern struct fdt_header two_roots;
> +extern struct fdt_header named_root;
>  #endif /* ! __ASSEMBLY */
> diff --git a/tests/trees.S b/tests/trees.S
> index e2380b7..95d599d 100644
> --- a/tests/trees.S
> +++ b/tests/trees.S
> @@ -298,3 +298,18 @@ two_roots_strings_end:
>  
>  two_roots_end:
>  
> +
> +        /* root node with a non-empty name */
> +        TREE_HDR(named_root)
> +	EMPTY_RSVMAP(named_root)
> +
> +named_root_struct:
> +	BEGIN_NODE("fake")
> +	END_NODE
> +	FDTLONG(FDT_END)
> +named_root_struct_end:
> +
> +named_root_strings:
> +named_root_strings_end:
> +
> +named_root_end:

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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