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Message-Id: <20190301210529.8218-1-daniel@iogearbox.net> Date: Fri, 1 Mar 2019 22:05:29 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: ast@...com Cc: afabre@...udflare.com, marek@...udflare.com, bpf@...r.kernel.org, netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net> Subject: [PATCH bpf] bpf: fix sanitation rewrite in case of non-pointers Marek reported that he saw an issue with the below snippet in that timing measurements where off when loaded as unpriv while results were reasonable when loaded as privileged: [...] uint64_t a = bpf_ktime_get_ns(); uint64_t b = bpf_ktime_get_ns(); uint64_t delta = b - a; if ((int64_t)delta > 0) { [...] Turns out there is a bug where a corner case is missing in the fix d3bd7413e0ca ("bpf: fix sanitation of alu op with pointer / scalar type from different paths"), namely fixup_bpf_calls() only checks whether aux has a non-zero alu_state, but it also needs to test for the case of BPF_ALU_NON_POINTER since in both occasions we need to skip the masking rewrite (as there is nothing to mask). Fixes: d3bd7413e0ca ("bpf: fix sanitation of alu op with pointer / scalar type from different paths") Reported-by: Marek Majkowski <marek@...udflare.com> Reported-by: Arthur Fabre <afabre@...udflare.com> Signed-off-by: Daniel Borkmann <daniel@...earbox.net> Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@mail.gmail.com/T/ --- [ Test case will be routed via bpf-next to avoid useless merge churn due to test_verifier rework in bpf-next. ] kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8f295b790297..5fcce2f4209d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6920,7 +6920,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) u32 off_reg; aux = &env->insn_aux_data[i + delta]; - if (!aux->alu_state) + if (!aux->alu_state || + aux->alu_state == BPF_ALU_NON_POINTER) continue; isneg = aux->alu_state & BPF_ALU_NEG_VALUE; -- 2.17.1
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