Commit 3612af78 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Alexei Starovoitov

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: default avatarMarek Majkowski <marek@cloudflare.com>
Reported-by: default avatarArthur Fabre <afabre@cloudflare.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@mail.gmail.com/T/Acked-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent d1a2930d
...@@ -6920,7 +6920,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) ...@@ -6920,7 +6920,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
u32 off_reg; u32 off_reg;
aux = &env->insn_aux_data[i + delta]; aux = &env->insn_aux_data[i + delta];
if (!aux->alu_state) if (!aux->alu_state ||
aux->alu_state == BPF_ALU_NON_POINTER)
continue; continue;
isneg = aux->alu_state & BPF_ALU_NEG_VALUE; isneg = aux->alu_state & BPF_ALU_NEG_VALUE;
......
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