On Tue, Mar 23, 2021 at 12:19:40PM +1300, Simon Glass wrote:
> At present it is possible to have two root nodes and even access nodes
> in the 'second' root. Such trees should not be considered valid. This
> 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@xxxxxxxxxxxx>
> Reported-by: Arie Haenel <arie.haenel@xxxxxxxxx>
> Reported-by: Julien Lenoir <julien.lenoir@xxxxxxxxx>
> ---
>
> libfdt/fdt_check.c | 7 +++++++
> tests/Makefile.tests | 4 +++-
> tests/dumptrees.c | 1 +
> tests/run_tests.sh | 2 +-
> tests/testdata.h | 1 +
> tests/trees.S | 19 +++++++++++++++++++
> 6 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/libfdt/fdt_check.c b/libfdt/fdt_check.c
> index 9ddfdbf..84870a5 100644
> --- a/libfdt/fdt_check.c
> +++ b/libfdt/fdt_check.c
> @@ -19,6 +19,7 @@ int fdt_check_full(const void *fdt, size_t bufsize)
> unsigned int depth = 0;
> const void *prop;
> const char *propname;
> + bool expect_end = false;
>
> if (bufsize < FDT_V1_SIZE)
> return -FDT_ERR_TRUNCATED;
> @@ -41,6 +42,10 @@ 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;
This should be -FDT_ERR_BADSTRUCTURE (since it's an error in the
format of the structure block), but otherwise this patch LGTM.
> +
> switch (tag) {
> case FDT_NOP:
> break;
> @@ -60,6 +65,8 @@ int fdt_check_full(const void *fdt, size_t bufsize)
> if (depth == 0)
> return -FDT_ERR_BADSTRUCTURE;
> depth--;
> + if (depth == 0)
> + expect_end = true;
> break;
>
> case FDT_PROP:
> diff --git a/tests/Makefile.tests b/tests/Makefile.tests
> index cb66c9f..fe5cae8 100644
> --- a/tests/Makefile.tests
> +++ b/tests/Makefile.tests
> @@ -32,7 +32,9 @@ LIB_TESTS_L = get_mem_rsv \
> fs_tree1
> LIB_TESTS = $(LIB_TESTS_L:%=$(TESTS_PREFIX)%)
>
> -LIBTREE_TESTS_L = truncated_property truncated_string truncated_memrsv
> +LIBTREE_TESTS_L = truncated_property truncated_string truncated_memrsv \
> + two_roots
> +
> LIBTREE_TESTS = $(LIBTREE_TESTS_L:%=$(TESTS_PREFIX)%)
>
> DL_LIB_TESTS_L = asm_tree_dump value-labels
> diff --git a/tests/dumptrees.c b/tests/dumptrees.c
> index aecb326..02ca092 100644
> --- a/tests/dumptrees.c
> +++ b/tests/dumptrees.c
> @@ -24,6 +24,7 @@ static struct {
> TREE(ovf_size_strings),
> TREE(truncated_property), TREE(truncated_string),
> TREE(truncated_memrsv),
> + TREE(two_roots)
> };
>
> #define NUM_TREES (sizeof(trees) / sizeof(trees[0]))
> diff --git a/tests/run_tests.sh b/tests/run_tests.sh
> index 4b8dada..82543fc 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; do
> + truncated_memrsv.dtb two_roots.dtb; do
> run_test check_full -n $bad
> done
> }
> diff --git a/tests/testdata.h b/tests/testdata.h
> index 0d08efb..d03f352 100644
> --- a/tests/testdata.h
> +++ b/tests/testdata.h
> @@ -55,4 +55,5 @@ extern struct fdt_header bad_prop_char;
> 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;
> #endif /* ! __ASSEMBLY */
> diff --git a/tests/trees.S b/tests/trees.S
> index efab287..e2380b7 100644
> --- a/tests/trees.S
> +++ b/tests/trees.S
> @@ -279,3 +279,22 @@ truncated_memrsv_rsvmap:
> truncated_memrsv_rsvmap_end:
>
> truncated_memrsv_end:
> +
> +
> + /* two root nodes */
> + TREE_HDR(two_roots)
> + EMPTY_RSVMAP(two_roots)
> +
> +two_roots_struct:
> + BEGIN_NODE("")
> + END_NODE
> + BEGIN_NODE("")
> + END_NODE
> + FDTLONG(FDT_END)
> +two_roots_struct_end:
> +
> +two_roots_strings:
> +two_roots_strings_end:
> +
> +two_roots_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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