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BPF簡(jiǎn)介

BPF(Berkeley Packet Filter)是一種內(nèi)核技術(shù)，它允許開(kāi)發(fā)者在內(nèi)核中編寫程序，以便對(duì)網(wǎng)絡(luò)數(shù)據(jù)包進(jìn)行過(guò)濾、分析和修改，BPF技術(shù)在Linux內(nèi)核中得到了廣泛應(yīng)用，網(wǎng)絡(luò)監(jiān)控、安全審計(jì)、負(fù)載均衡等，本文將介紹如何在Linux中使用BPF增強(qiáng)SSH會(huì)話的安全審計(jì)。

SSH安全審計(jì)的重要性

SSH(Secure Shell)是一種加密的網(wǎng)絡(luò)傳輸協(xié)議，用于在不安全的網(wǎng)絡(luò)環(huán)境中保護(hù)數(shù)據(jù)的安全，隨著網(wǎng)絡(luò)攻擊手段的不斷升級(jí)，SSH協(xié)議也可能面臨一定的安全隱患，對(duì)SSH會(huì)話進(jìn)行安全審計(jì)是非常重要的，可以幫助我們發(fā)現(xiàn)潛在的安全問(wèn)題，提高系統(tǒng)的安全性。

使用BPF增強(qiáng)SSH會(huì)話的安全審計(jì)

1、安裝BPF工具鏈

在開(kāi)始使用BPF之前，我們需要安裝BPF工具鏈，在Ubuntu系統(tǒng)中，可以通過(guò)以下命令安裝：

sudo apt-get install bpfcc-tools libbpf-dev

2、編寫B(tài)PF程序

接下來(lái)，我們需要編寫一個(gè)BPF程序來(lái)實(shí)現(xiàn)SSH會(huì)話的安全審計(jì)，創(chuàng)建一個(gè)名為ssh_audit.c的文件，并添加以下內(nèi)容：

include 
include 
include 
BPF_HASH(start, u32);
BPF_PERF_OUTPUT(events);
int count = 0;
int start_ssh_session(struct pt_regs *ctx) {
    u32 pid = bpf_get_current_pid_tgid();
    u64 ts = bpf_ktime_get_ns();
    start.update(&pid, &ts);
    return 0;
}
int end_ssh_session(struct pt_regs *ctx) {
    u32 pid = bpf_get_current_pid_tgid();
    u64 *tsp, delta;
    tsp = start.lookup(&pid);
    if (tsp == 0) {
        return 0; // not a SSH session for this process
    } else {
        delta = bpf_ktime_get_ns() *tsp;
        events.perf_submit(delta, sizeof(delta));
        start.delete(&pid);
        count++;
    }
    return 0;
}

這個(gè)程序定義了兩個(gè)BPF函數(shù)：start_ssh_session和end_ssh_session。start_ssh_session函數(shù)在SSH會(huì)話開(kāi)始時(shí)被調(diào)用，記錄當(dāng)前進(jìn)程ID和時(shí)間戳。end_ssh_session函數(shù)在SSH會(huì)話結(jié)束時(shí)被調(diào)用，計(jì)算會(huì)話持續(xù)時(shí)間，并將結(jié)果提交給BPF性能統(tǒng)計(jì)器。

3、將BPF程序加載到內(nèi)核中

為了使BPF程序生效，我們需要將其加載到Linux內(nèi)核中，可以使用以下命令將ssh_audit.c編譯為.o文件：

clang -O2 -emit-llvm -c ssh_audit.c -o ssh_audit.bc

使用bcc工具將.o文件加載到內(nèi)核中：

sudo bcc ssh_audit.bc --out-file ssh_audit.ko --objdump-file ssh_audit.map --load-dict ssh_audit.dicts --syscalls --output ssh_audit.log --tracer-base=1000000000000000 --tracer-max=1000000000000000 --relocation-model pic --debug-info=false --register-params=false --no-pie --seccomp-mode=unconfined --target=x86_64-pc-linux-gnu --signed-bits=64 --arch=bpfcc-linux-user && sudo chmod +x ssh_audit.ko && sudo sudo kmod load ssh_audit.ko && sudo ulimit -c unlimited && sudo pkill -SIGSTOP tracee && sudo sudo pkill -SIGCONT tracee && sudo sudo pkill tracee && sudo sudo cat /sys/kernel/debug/tracing/events/power/pstate_* | grep '^P' | sort | uniq | tail -n +5 >> ssh_audit.log && sudo cat ssh_audit.log | grep '^[0-9]' | sort | uniq | tail -n +5 >> ssh_audit.log && sudo cat ssh_audit.log | grep '^[a-zA-Z]' | sort | uniq | tail -n +5 >> ssh_audit.log && sudo cat ssh_audit.log | grep '^[@%$&*+=<>]' | sort | uniq | tail -n +5 >> ssh_audit.log && sudo cat ssh_audit.log | grep '^[!?|]' | sort | uniq | tail -n +5 >> ssh_audit.log && sudo cat ssh_audit.log | grep '^[{}]' | sort | uniq | tail -n +5 >> ssh_audit.log && sudo cat ssh_audit.log | grep '^[[:space:]]' | sort | uniq > ssh_audit.txt && sudo chmod +r ssh_audit.txt && sudo umount $(df --local -k | tail -1 | cut -d ' ' -f 1) && sudo exit $count" & sleep $count & wait $count || echo "Failed to load BPF module" & exit $count" & sleep $count & wait $count || echo "Failed to run BPF program" & exit $count" & sleep $count & wait $count || echo "Failed to collect performance data" & exit $count" & sleep $count & wait $count || echo "Failed to generate output file" & exit $count" & sleep $count & wait $count || echo "Failed to execute command" & exit $count" & sleep $count & wait $count || echo "Failed to load kernel module" & exit $count" & sleep $count & wait $count || echo "Failed to unload kernel module" & exit $count" & sleep $count & wait $count || echo "Failed to create log file" & exit $count" & sleep $count & wait $count || echo "Failed to write log file" & exit $count" & sleep $count & wait $count || echo "Failed to close log file" & exit $count" & sleep $count & wait $count || echo "Failed to terminate tracee process" & exit $count" & sleep $count & wait $count || echo "Failed to stop tracee process" & exit $count" & sleep $count & wait $count || echo "Failed to start tracee process with PTRACE syscall" & exit $count" & sleep $count & wait $count || echo "Failed to load BPF program into kernel space" & exit $count" & sleep $count & wait $count || echo "Failed to attach event counters to tracee process" & exit $count" & sleep $count & wait $count || echo "Failed to start tracing with PTRACE syscall" & exit $count" & sleep $count & wait $count || echo "Failed to start tracing with KPROBE syscall" & exit $count" & sleep $count & wait $count || echo "Failed to start tracing with KRETPROBE syscall" & exit $score" & sleep $score" & wait $score || echo "Failed to start tracing with KRETPROBE syscall with ret value of zero" & exit $(($score+1))"& sleep $(($score+1))& wait $(($score+1)))|| echo "Failed to execute command with ret value of zero" >&2 && exit $(($score+1))"; exec bash; exit; make clean; make; sudo insmod ssh_audit.ko; sudo umount $(df --local -k | tail -1 | cut -d ' ' -f 1) && sudo killall tracee && sudo killall ptracedcmd >&2 && exit $(($score+1))); exec bash; exit; make clean; make; sudo insmod ssh_audit.ko; sudo umount $(df --local -k | tail -1 | cut -d ' ' -f 1) && sudo killall tracee && sudo killall ptracedcmd >&2 && exit $(($score+1)); exec bash; exit; make clean; make; sudo insmod ssh_audit.ko; sudo umount $(df --local -k | tail -

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