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    SubjectRe: [PATCH AUTOSEL 5.14 101/252] bpf: Fix off-by-one in tail call count limiting
    Sasha,

    This patch should not be applied to any of the stable kernels. It was
    reverted in f9dabe016b63 ("bpf: Undo off-by-one in interpreter tail
    call count limit").

    I don't think it will pass the CI selftests so maybe it wouldn't be
    applied anyway, but nevertheless I want to inform you about it.

    Johan

    On Thu, Sep 9, 2021 at 1:43 PM Sasha Levin <sashal@kernel.org> wrote:
    >
    > From: Johan Almbladh <johan.almbladh@anyfinetworks.com>
    >
    > [ Upstream commit b61a28cf11d61f512172e673b8f8c4a6c789b425 ]
    >
    > Before, the interpreter allowed up to MAX_TAIL_CALL_CNT + 1 tail calls.
    > Now precisely MAX_TAIL_CALL_CNT is allowed, which is in line with the
    > behavior of the x86 JITs.
    >
    > Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
    > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    > Acked-by: Yonghong Song <yhs@fb.com>
    > Link: https://lore.kernel.org/bpf/20210728164741.350370-1-johan.almbladh@anyfinetworks.com
    > Signed-off-by: Sasha Levin <sashal@kernel.org>
    > ---
    > kernel/bpf/core.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
    > index 0a28a8095d3e..82af6279992d 100644
    > --- a/kernel/bpf/core.c
    > +++ b/kernel/bpf/core.c
    > @@ -1564,7 +1564,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
    >
    > if (unlikely(index >= array->map.max_entries))
    > goto out;
    > - if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
    > + if (unlikely(tail_call_cnt >= MAX_TAIL_CALL_CNT))
    > goto out;
    >
    > tail_call_cnt++;
    > --
    > 2.30.2
    >

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