Commit 3612af78 authored Mar 01, 2019 by Daniel Borkmann Committed by Alexei Starovoitov Mar 01, 2019

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
d3bd7413 ("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: d3bd7413 ("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>

parent d1a2930d

kernel/bpf/verifier.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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;