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* [PATCH] libsepol/cil: Fix heap-use-after-free when using optional blockinherit
@ 2021-02-01 14:24 James Carter
  2021-02-01 22:08 ` Nicolas Iooss
  0 siblings, 1 reply; 6+ messages in thread
From: James Carter @ 2021-02-01 14:24 UTC (permalink / raw)
  To: selinux; +Cc: nicolas.iooss, James Carter

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>
---
 libsepol/cil/src/cil_build_ast.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/libsepol/cil/src/cil_build_ast.c b/libsepol/cil/src/cil_build_ast.c
index 02481558..3d8367fe 100644
--- a/libsepol/cil/src/cil_build_ast.c
+++ b/libsepol/cil/src/cil_build_ast.c
@@ -283,6 +283,23 @@ void cil_destroy_blockinherit(struct cil_blockinherit *inherit)
 		return;
 	}
 
+	if (inherit->block != NULL && inherit->block->bi_nodes != NULL) {
+		struct cil_tree_node *node;
+		struct cil_list_item *item;
+		int found = CIL_FALSE;
+
+		cil_list_for_each(item, inherit->block->bi_nodes) {
+			node = item->data;
+			if (node->data == inherit) {
+				found = CIL_TRUE;
+				break;
+			}
+		}
+		if (found == CIL_TRUE) {
+			cil_list_remove(inherit->block->bi_nodes, CIL_NODE, node, CIL_FALSE);
+		}
+	}
+
 	free(inherit);
 }
 
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [PATCH] libsepol/cil: fix heap-use-after-free when using optional blockinherit
@ 2021-01-31 23:12 Nicolas Iooss
  2021-02-01 14:26 ` James Carter
  0 siblings, 1 reply; 6+ messages in thread
From: Nicolas Iooss @ 2021-01-31 23:12 UTC (permalink / raw)
  To: selinux

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).

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
---
 libsepol/cil/src/cil_tree.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/libsepol/cil/src/cil_tree.c b/libsepol/cil/src/cil_tree.c
index 886412d1b974..72c4892de707 100644
--- a/libsepol/cil/src/cil_tree.c
+++ b/libsepol/cil/src/cil_tree.c
@@ -223,11 +223,20 @@ void cil_tree_node_init(struct cil_tree_node **node)
 void cil_tree_node_destroy(struct cil_tree_node **node)
 {
 	struct cil_symtab_datum *datum;
+	struct cil_blockinherit *inherit;
 
 	if (node == NULL || *node == NULL) {
 		return;
 	}
 
+	if ((*node)->flavor == CIL_BLOCKINHERIT) {
+		inherit = (*node)->data;
+		if (inherit->block != NULL && inherit->block->bi_nodes != NULL) {
+			// Unlink the blockinherit from the block
+			cil_list_remove(inherit->block->bi_nodes, CIL_NODE, *node, CIL_FALSE);
+		}
+	}
+
 	if ((*node)->flavor >= CIL_MIN_DECLARATIVE) {
 		datum = (*node)->data;
 		cil_symtab_datum_remove_node(datum, *node);
-- 
2.30.0


^ permalink raw reply related	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-02-03  8:24 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-02-01 14:24 [PATCH] libsepol/cil: Fix heap-use-after-free when using optional blockinherit James Carter
2021-02-01 22:08 ` Nicolas Iooss
2021-02-02 21:14   ` James Carter
2021-02-03  8:23     ` Nicolas Iooss
  -- strict thread matches above, loose matches on Subject: below --
2021-01-31 23:12 [PATCH] libsepol/cil: fix " Nicolas Iooss
2021-02-01 14:26 ` James Carter

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