On Fri, May 01, 2020 at 11:56:22AM -0700, Andrii Nakryiko wrote: > If bpf_link_prime() succeeds to allocate new anon file, but then fails to > allocate ID for it, link priming is considered to be failed and user is > supposed ot be able to directly kfree() bpf_link, because it was never exposed > to user-space. > > But at that point file already keeps a pointer to bpf_link and will eventually > call bpf_link_release(), so if bpf_link was kfree()'d by caller, that would > lead to use-after-free. > > Fix this by first allocating ID and only then allocating file. Adding ID to > link_idr is ok, because link at that point still doesn't have its ID set, so > no user-space process can create a new FD for it. Acked-by: Martin KaFai Lau <kafai@xxxxxx>
