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Message-ID: <CAF=yD-LzUjhG7f=fXqomB_wpzThZ1J7W7V1FzTHQrYw-a7fT9g@mail.gmail.com>
Date: Thu, 23 Feb 2017 12:20:23 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Chenbo Feng <chenbofeng.kernel@...il.com>
Cc: Network Development <netdev@...r.kernel.org>,
Chenbo Feng <fengc@...gle.com>
Subject: Re: [PATCH net-next v3 3/3] A Sample of using socket cookie and uid
for traffic monitoring
> +/* This test is a demo of using get_socket_uid and get_socket_cookie
> + * helper function to do per socket based network traffic monitoring.
> + * It requires iptable version higher then 1.6.1. to load pined eBPF
> + * program into the xt_bpf match.
iptable -> iptables (everywhre
pined -> pinned
> + * Clean up: if using shell script, the script file will delete the iptables
> + * rule and unmount the bpf program when exit. Else the iptables rule need
> + * to be deleted using:
> + * iptables -D INPUT -m bpf --object-pinned ${mnt_dir}/bpf_prog -j ACCEPT
this is already in the wrapper script
> + struct bpf_insn prog[] = {
> + /*
> + * it for future usage. value stored in R6 to R10 will not be
> + * reset after a bpf helper function call.
garbled comment
> + */
> + BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
> + /*
> + * pc1: BPF_FUNC_get_socket_cookie takes one parameter,
> + * R1: sk_buff
> + */
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> + BPF_FUNC_get_socket_cookie),
> + /* pc2-4: save &socketCookie to r7 for future usage*/
> + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_0, -8),
> + BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
> + /*
> + * pc5-8: set up the registers for BPF_FUNC_map_lookup_elem,
> + * it takes two parameters (R1: map_fd, R2: &socket_cookie)
> + */
> + BPF_LD_MAP_FD(BPF_REG_1, map_fd),
> + BPF_MOV64_REG(BPF_REG_2, BPF_REG_7),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> + BPF_FUNC_map_lookup_elem),
> + /*
> + * pc9. if r0 != 0x0, go to pc+14, since we have the cookie
> + * stored already
> + * Otherwise do pc10-22 to setup a new data entry.
> + */
> + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 14),
> + BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> + BPF_FUNC_get_socket_uid),
> + /*
> + * Place a struct stats in the R10 stack and sequentially
> + * place the member value into the memory. Packets value
> + * is set by directly place a IMM value 1 into the stack.
> + */
> + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_0,
> + -32 + offsetof(struct stats, uid)),
> + BPF_ST_MEM(BPF_DW, BPF_REG_10,
> + -32 + offsetof(struct stats, packets), 1),
> + /*
> + * __sk_buff is a special struct used for eBPF program to
> + * directly access some sk_buff field.
> + */
> + BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_6,
> + offsetof(struct __sk_buff, len)),
> + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1,
> + -32 + offsetof(struct stats, bytes)),
> + /*
> + * add new map entry using BPF_FUNC_map_update_elem, it takes
> + * 4 parameters (R1: map_fd, R2: &socket_cookie, R3: &stats)
R4: flags
> + */
> + BPF_LD_MAP_FD(BPF_REG_1, map_fd),
> + BPF_MOV64_REG(BPF_REG_2, BPF_REG_7),
> + BPF_MOV64_REG(BPF_REG_3, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, -32),
> + BPF_MOV64_IMM(BPF_REG_4, 0),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> + BPF_FUNC_map_update_elem),
> + BPF_JMP_IMM(BPF_JA, 0, 0, 5),
> + /*
> + * pc24-30 update the packet info to a exist data entry, it can
> + * be done by directly write to pointers instead of using
> + * BPF_FUNC_map_update_elem helper function
> + */
> + BPF_MOV64_REG(BPF_REG_9, BPF_REG_0),
> + BPF_MOV64_IMM(BPF_REG_1, 1),
> + BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_9, BPF_REG_1,
> + offsetof(struct stats, packets), 0),
BPF_STX_XADD here and below
> + BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_6,
> + offsetof(struct __sk_buff, len)),
> + BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_9, BPF_REG_1,
> + offsetof(struct stats, bytes), 0),
> + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_6,
> + offsetof(struct __sk_buff, len)),
No requirement to return len. It goes unused, can just return non-zero
immediate.
> +static void prog_attach_iptables(char *file)
> +{
> + int ret;
> + char rules[100];
> +
> + if (bpf_obj_pin(prog_fd, file))
> + error(1, errno, "bpf_obj_pin");
> + sprintf(rules, "iptables -A INPUT -m bpf --object-pinned %s -j ACCEPT",
> + file);
this is a test, but still: unsafe to pass user input unchecked to sprintf
> + printf("cookie: %u, uid: 0x%x, Pakcet Count: %lu,"
Packet
> diff --git a/samples/bpf/run_cookie_uid_helper_example.sh b/samples/bpf/run_cookie_uid_helper_example.sh
> new file mode 100755
> index 0000000..a7a6208
> --- /dev/null
> +++ b/samples/bpf/run_cookie_uid_helper_example.sh
> @@ -0,0 +1,14 @@
> +#!/bin/bash
> +local_dir="$(pwd)"
> +root_dir=$local_dir/../..
> +mnt_dir=/sys/fs/bpf
Don't modify state outside the test environment. Perhaps use a temporary dir:
mnt_dir=$(mktemp -d --tmp)
and remove it in on_exit
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