Commit a042c21a authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Greg Kroah-Hartman

bpf: fix sanitation rewrite in case of non-pointers

commit 3612af78 upstream.

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>
Signed-off-by: default avatarBalbir Singh <sblbir@amzn.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 12462c88
...@@ -4771,7 +4771,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) ...@@ -4771,7 +4771,8 @@ 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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