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Message-ID: <CAJ8uoz0RXAFPfu1v_1UuV-iUZ846ZbHNNB=oCQ=sV=pbLSzvxw@mail.gmail.com> Date: Fri, 2 Sep 2022 08:15:34 +0200 From: Magnus Karlsson <magnus.karlsson@...il.com> To: Ian Rogers <irogers@...gle.com> Cc: Björn Töpel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v1] selftests/xsk: Avoid use-after-free on ctx On Thu, Sep 1, 2022 at 10:56 PM Ian Rogers <irogers@...gle.com> wrote: > > The put lowers the reference count to 0 and frees ctx, reading it > afterwards is invalid. Move the put after the uses and determine the > last use by the reference count being 1. Thanks for spotting and fixing this Ian. Acked-by: Magnus Karlsson <magnus.karlsson@...el.com> > Fixes: 39e940d4abfa ("selftests/xsk: Destroy BPF resources only when ctx refcount drops to 0") > Signed-off-by: Ian Rogers <irogers@...gle.com> > --- > tools/testing/selftests/bpf/xsk.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/bpf/xsk.c b/tools/testing/selftests/bpf/xsk.c > index f2721a4ae7c5..0b3ff49c740d 100644 > --- a/tools/testing/selftests/bpf/xsk.c > +++ b/tools/testing/selftests/bpf/xsk.c > @@ -1237,15 +1237,15 @@ void xsk_socket__delete(struct xsk_socket *xsk) > ctx = xsk->ctx; > umem = ctx->umem; > > - xsk_put_ctx(ctx, true); > - > - if (!ctx->refcount) { > + if (ctx->refcount == 1) { > xsk_delete_bpf_maps(xsk); > close(ctx->prog_fd); > if (ctx->has_bpf_link) > close(ctx->link_fd); > } > > + xsk_put_ctx(ctx, true); > + > err = xsk_get_mmap_offsets(xsk->fd, &off); > if (!err) { > if (xsk->rx) { > -- > 2.37.2.789.g6183377224-goog >
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