Re: [PATCH 5/6] libsepol/cil: fix out-of-bound read in cil_print_recursive_blockinherit

[James Carter <jwcart2@gmail.com>]

On Wed, Dec 30, 2020 at 5:09 AM Nicolas Iooss <nicolas.iooss@m4x.org> wrote:
>
> OSS-Fuzz found a heap buffer overflow (out-of-bound reads) when the CIL
> compiler tries to report a recursive blockinherit with an optional
> block:
>
>     $ echo '(block b (optional o (blockinherit b)))' > tmp.cil
>     $ secilc tmp.cil
>     Segmentation fault (core dumped)
>
> This is because cil_print_recursive_blockinherit() assumes that all
> nodes are either CIL_BLOCK or CIL_BLOCKINHERIT. Add support for other
> block kinds, using cil_node_to_string() to show them.
>
> Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28462
> Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>

Acked-by: James Carter <jwcart2@gmail.com>

> ---
>  libsepol/cil/src/cil_resolve_ast.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/libsepol/cil/src/cil_resolve_ast.c b/libsepol/cil/src/cil_resolve_ast.c
> index f6deb1002fbd..ecd05dfa5dab 100644
> --- a/libsepol/cil/src/cil_resolve_ast.c
> +++ b/libsepol/cil/src/cil_resolve_ast.c
> @@ -2343,11 +2343,13 @@ void cil_print_recursive_blockinherit(struct cil_tree_node *bi_node, struct cil_
>         for (curr = bi_node; curr != terminating_node; curr = curr->parent) {
>                 if (curr->flavor == CIL_BLOCK) {
>                         cil_list_prepend(trace, CIL_NODE, curr);
> -               } else {
> +               } else if (curr->flavor == CIL_BLOCKINHERIT) {
>                         if (curr != bi_node) {
>                                 cil_list_prepend(trace, CIL_NODE, NODE(((struct cil_blockinherit *)curr->data)->block));
>                         }
>                         cil_list_prepend(trace, CIL_NODE, curr);
> +               } else {
> +                       cil_list_prepend(trace, CIL_NODE, curr);
>                 }
>         }
>         cil_list_prepend(trace, CIL_NODE, terminating_node);
> @@ -2356,8 +2358,12 @@ void cil_print_recursive_blockinherit(struct cil_tree_node *bi_node, struct cil_
>                 curr = item->data;
>                 if (curr->flavor == CIL_BLOCK) {
>                         cil_tree_log(curr, CIL_ERR, "block %s", DATUM(curr->data)->name);
> -               } else {
> +               } else if (curr->flavor == CIL_BLOCKINHERIT) {
>                         cil_tree_log(curr, CIL_ERR, "blockinherit %s", ((struct cil_blockinherit *)curr->data)->block_str);
> +               } else if (curr->flavor == CIL_OPTIONAL) {
> +                       cil_tree_log(curr, CIL_ERR, "optional %s", DATUM(curr->data)->name);
> +               } else {
> +                       cil_tree_log(curr, CIL_ERR, "%s", cil_node_to_string(curr));
>                 }
>         }
>
> --
> 2.29.2
>