On 10/05/2018 21:16, Roman Kagan wrote:
If an IDR contains a single entry at index==0, the underlying radix tree has a single item in its root node, in which case __radix_tree_lookup(index!=0) doesn't set its *@nodep argument (in addition to returning NULL).
However, the tree itself is not empty, i.e. the tree root doesn't have IDR_FREE tag.
As a result, on an attempt to remove an index!=0 entry from such an IDR, radix_tree_delete_item doesn't return early and calls __radix_tree_delete with invalid parameters which are then dereferenced.
Reported-by: syzbot+35666cba7f0a337e2e79@syzkaller.appspotmail.com Signed-off-by: Roman Kagan rkagan@virtuozzo.com
lib/radix-tree.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/lib/radix-tree.c b/lib/radix-tree.c index da9e10c827df..10ff1bfae952 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -2040,8 +2040,9 @@ void *radix_tree_delete_item(struct radix_tree_root *root, void *entry; entry = __radix_tree_lookup(root, index, &node, &slot);
- if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
get_slot_offset(node, slot))))
- if (!entry && (!is_idr(root) || !node ||
node_tag_get(root, node, IDR_FREE,get_slot_offset(node, slot))))if (item && entry != item)
I cannot really vouch for the patch, but if it is correct it's definitely stuff for stable. The KVM testcase is only for 4.17-rc but this is a really nasty bug in a core data structure.
Cc: stable@vger.kernel.org
Should radix-tree be compilable in userspace, so that we can add unit tests for it?...
Paolo