Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit ceefbc96 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Daniel Borkmann
Browse files

bpf: add per-insn complexity limit 



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: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarEdward Cree <ecree@solarflare.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 4f7b3e82

kernel/bpf/verifier.c

+6 −1
Original line number Diff line number Diff line
@@ -175,6 +175,7 @@ struct bpf_verifier_stack_elem { 


#define BPF_COMPLEXITY_LIMIT_INSNS	131072

#define BPF_COMPLEXITY_LIMIT_STACK	1024

#define BPF_COMPLEXITY_LIMIT_STATES	64



#define BPF_MAP_PTR_UNPRIV	1UL

#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 *sl;

	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];

	if (!sl)
@@ -5074,8 +5075,12 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx) 
			return 1;

		}

		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.

	 * 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)