bpf: add per-insn complexity limit (ceefbc96) · Commits · 戴 / test

malicious bpf program may try to force the verifier to remember a lot of distinct verifier states. Put a limit to number of per-insn 'struct bpf_verifier_state'. Note that hitting the limit doesn't reject the program. It potentially makes the verifier do more steps to analyze the program. It means that malicious programs will hit BPF_COMPLEXITY_LIMIT_INSNS sooner instead of spending cpu time walking long link list. The limit of BPF_COMPLEXITY_LIMIT_STATES==64 affects cilium progs with slight increase in number of "steps" it takes to successfully verify the programs: before after bpf_lb-DLB_L3.o 1940 1940 bpf_lb-DLB_L4.o 3089 3089 bpf_lb-DUNKNOWN.o 1065 1065 bpf_lxc-DDROP_ALL.o 28052 | 28162 bpf_lxc-DUNKNOWN.o 35487 | 35541 bpf_netdev.o 10864 10864 bpf_overlay.o 6643 6643 bpf_lcx_jit.o 38437 38437 But it also makes malicious program to be rejected in 0.4 seconds vs 6.5 Hence apply this limit to unprivileged programs only. Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Daniel Borkmann <daniel@iogearbox.net> Acked-by:

Edward Cree <ecree@solarflare.com> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/verifier.c

+6 −1

Original line number	Original line	Diff line number	Diff line
	@@ -175,6 +175,7 @@ struct bpf_verifier_stack_elem {

	#define BPF_COMPLEXITY_LIMIT_INSNS 131072		#define BPF_COMPLEXITY_LIMIT_INSNS 131072
	#define BPF_COMPLEXITY_LIMIT_STACK 1024		#define BPF_COMPLEXITY_LIMIT_STACK 1024
			#define BPF_COMPLEXITY_LIMIT_STATES 64

	#define BPF_MAP_PTR_UNPRIV 1UL		#define BPF_MAP_PTR_UNPRIV 1UL
	#define BPF_MAP_PTR_POISON ((void *)((0xeB9FUL << 1) + \		#define BPF_MAP_PTR_POISON ((void *)((0xeB9FUL << 1) + \
	@@ -5047,7 +5048,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
	struct bpf_verifier_state_list *new_sl;		struct bpf_verifier_state_list *new_sl;
	struct bpf_verifier_state_list *sl;		struct bpf_verifier_state_list *sl;
	struct bpf_verifier_state cur = env->cur_state, new;		struct bpf_verifier_state cur = env->cur_state, new;
	int i, j, err;		int i, j, err, states_cnt = 0;

	sl = env->explored_states[insn_idx];		sl = env->explored_states[insn_idx];
	if (!sl)		if (!sl)
	@@ -5074,8 +5075,12 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
	return 1;		return 1;
	}		}
	sl = sl->next;		sl = sl->next;
			states_cnt++;
	}		}

			if (!env->allow_ptr_leaks && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
			return 0;

	/* there were no equivalent states, remember current one.		/* there were no equivalent states, remember current one.
	* technically the current state is not proven to be safe yet,		* technically the current state is not proven to be safe yet,
	* but it will either reach outer most bpf_exit (which means it's safe)		* but it will either reach outer most bpf_exit (which means it's safe)

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