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. Cc: stable@xxxxxxxxxxxxxxx Should radix-tree be compilable in userspace, so that we can add unit tests for it?... Paolo
