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@xxxxxxxxxxxxxx>
Reported-by: Arthur Fabre <afabre@xxxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@xxxxxxxxxxxxxx/T/
---
[ Test case will be routed via bpf-next to avoid useless merge churn
due to test_verifier rework in bpf-next. ]
kernel/bpf/verifier.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8f295b790297..5fcce2f4209d 100644
--- 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;
--
2.17.1
