In the Linux kernel, the following vulnerability has been resolved: bpf: account for current...

In the Linux kernel, the following vulnerability has been resolved:

bpf: account for current allocated stack depth in widen_imprecise_scalars()

The usage pattern for widen_imprecise_scalars() looks as follows:

prev_st = find_prev_entry(env, ...);
queued_st = push_stack(...);
widen_imprecise_scalars(env, prev_st, queued_st);

Where prev_st is an ancestor of the queued_st in the explored states tree. This ancestor is not guaranteed to have same allocated stack depth as queued_st. E.g. in the following case:

def main():
  for i in 1..2:
    foo(i)        // same callsite, differnt param

def foo(i):
  if i == 1:
    use 128 bytes of stack
  iterator based loop

Here, for a second 'foo' call prev_st->allocated_stack is 128, while queued_st->allocated_stack is much smaller. widen_imprecise_scalars() needs to take this into account and avoid accessing bpf_verifier_state->frame[*]->stack out of bounds.