bpf: fix sanitation rewrite in case of non-pointers

borkmann · Alexei Starovoitov · commit 3612af783cf5 · 2019-03-01T21:24:08.000-08:00
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 d3bd741 ("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: d3bd741 ("bpf: fix sanitation of alu op with pointer / scalar type from different paths") Reported-by: Marek Majkowski <marek@cloudflare.com> Reported-by: Arthur Fabre <afabre@cloudflare.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@mail.gmail.com/T/ Acked-by: Song Liu <songliubraving@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git 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;
