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

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.

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于widen_imprecise_scalars未考虑当前分配的堆栈深度，可能导致越界访问。

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