In the Linux kernel, the following vulnerability has been resolved:net/l2tp: fix warning in l2tp_exit_net found by syzbotIn l2tp's net exit handler, we check that an IDR is empty beforedestroying it: WARN_ON_ONCE(!idr_is_empty(&pn->l2tp_tunnel_idr)); idr_destroy(&pn->l2tp_tunnel_idr);By forcing memory allocation failures in idr_alloc_32, syzbot is ableto provoke a condition where idr_is_empty returns false despite therebeing no items in the IDR. This turns out to be because the radix treeof the IDR contains only internal radix-tree nodes and it is this thatcauses idr_is_empty to return false. The internal nodes are cleaned byidr_destroy.Use idr_for_each to check that the IDR is empty instead ofidr_is_empty to avoid the problem.
