commit eba0ffee01ee11bb4fc3f6505d9cf69693088621
author James Carter <jwcart2@gmail.com> Tue Feb 02 15:54:17 2021 -0500
committer Petr Lautrbach <plautrba@redhat.com> Wed Feb 03 10:44:01 2021 +0100
tree 381540871a37b63606aa5db6410ef7b36f35773b
parent 1048f8d329a0e34a2529b3376fb085c5e6b3db0d

libsepol/cil: Fix heap-use-after-free when using optional blockinherit

This is based on a patch by Nicolas Iooss. He writes:
    When secilc compiles the following policy:

        (block b1
            (optional o1
                (blockinherit b1)
                (blockinherit x)
            )
        )

    it disables the optional block at pass 3 (CIL_PASS_BLKIN_LINK)
    because the block "x" does not exist.
    __cil_resolve_ast_last_child_helper() calls
    cil_tree_children_destroy() on the optional block, which destroys
    the two blockinherit statements. But the (blockinherit b1) node
    was referenced inside (block b1) node, in its block->bi_nodes list.
    Therefore, when this list is used at pass 4 (CIL_PASS_BLKIN_COPY),
    it contains a node which was freed: this triggers a use-after-free
    issue

    Fix this issue by removing blockinherit nodes from their lists of
    nodes block->bi_nodes when they are being destroyed. As
    cil_destroy_blockinherit() does not have a reference to the node
    containing the blockinherit data, implement this new logic in
    cil_tree_node_destroy().

    This issue was found while investigating a testcase from an OSS-Fuzz
    issue which seems unrelated (a Null-dereference READ in
    cil_symtab_get_datum,
    https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=29861).

Reported-by: Nicolas Iooss <nicolas.iooss@m4x.org>
Signed-off-by: James Carter <jwcart2@gmail.com>
Acked-by: Nicolas Iooss <nicolas.iooss@m4x.org>