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Message-ID: <e1250fdc-96f7-e020-eaff-7e0b67be9ead@iogearbox.net> Date: Sat, 2 Mar 2019 00:22:59 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: Song Liu <liu.song.a23@...il.com> Cc: Alexei Starovoitov <ast@...com>, afabre@...udflare.com, Marek Majkowski <marek@...udflare.com>, bpf@...r.kernel.org, Networking <netdev@...r.kernel.org> Subject: Re: [PATCH bpf] bpf: fix sanitation rewrite in case of non-pointers On 03/02/2019 12:18 AM, Song Liu wrote: > On Fri, Mar 1, 2019 at 1:06 PM Daniel Borkmann <daniel@...earbox.net> wrote: >> >> 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) > > alu_state is a bitmap. Shall we check "aux->alu_state & > BPF_ALU_NON_POINTER" here? The state in this case can only ever be BPF_ALU_NON_POINTER, any other setting from sanitize_val_alu() would be a violation.
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