[PATCH v2 1/2] bpf: reject stack-argument callback subprograms

Helper callbacks enter BPF subprograms through bpf_callback_t, whose
runtime ABI supplies five arguments. BTF validation nevertheless permits
static callback subprograms to declare more than five arguments when JIT
stack arguments are supported.

This lets verifier state for a callback use outgoing stack argument slots
prepared at the helper call site. The helper does not pass those slots. On
x86-64, callback loads of arguments seven and later therefore read the
helper native frame instead of the synthetic values checked by the
verifier. KASAN reports a slab OOB write.

Reject callback subprograms with incoming stack arguments when processing
callback calls.

Fixes: 0f6bd5e7a804 ("bpf: Support stack arguments for bpf functions")
Assisted-by: Codex:gpt-5
Signed-off-by: Jérémy Jean <[email protected]>
---
 kernel/bpf/verifier.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fdc5fbb1f78c..5fcefc0eaba0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9285,6 +9285,8 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins
 	err = btf_check_subprog_call(env, subprog, caller->regs);
 	if (err == -EFAULT)
 		return err;
+	if (bpf_in_stack_arg_cnt(&env->subprog_info[subprog]))
+		return -EINVAL;
 
 	/* set_callee_state is used for direct subprog calls, but we are
 	 * interested in validating only BPF helpers that can call subprogs as
-- 
2.47.3