Re: [PATCH] idr: fix invalid ptr dereference on item delete
From: Paolo Bonzini
Date: Thu May 10 2018 - 19:55:05 EST
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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
> 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))))
> return NULL;
> 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.
Should radix-tree be compilable in userspace, so that we can add unit
tests for it?...