bpf: fix sanitation rewrite in case of non-pointers

commit 3612af783cf52c74a031a2f11b82247b2599d3cd 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
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@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>
Signed-off-by: Balbir Singh <sblbir@amzn.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 87b1293f20d629ec3dd13a953f809bf5fe5cab25..a4875ff0bab197f8e71aa0b0d3fdea141e55c5a6 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4771,7 +4771,8 @@ 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;