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Date: Fri, 1 May 2020 15:52:55 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Martin KaFai Lau <kafai@...com> Cc: Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii.nakryiko@...il.com>, Kernel Team <kernel-team@...com>, syzbot+39b64425f91b5aab714d@...kaller.appspotmail.com Subject: Re: [PATCH v2 bpf-next] bpf: fix use-after-free of bpf_link when priming half-fails On Fri, May 1, 2020 at 1:00 PM Martin KaFai Lau <kafai@...com> wrote: > > 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@...com> Applied. Thanks
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