\u770b\u770blinux\u5b9e\u73b0\u7684\u4ee3\u7801\uff0c\u57fa\u672c\u4e0a\u662f\u8fd9\u6837\u5b9e\u73b0\u7684\u3002<\/p>\n
\tInt sk_run_filter(struct sk_buff *skb,struct sock_filter *filter,int flen)\r\n{\r\n\t..\/\/\u5b9a\u4e49\u4e2d\u95f4\u53d8\u91cf\uff0c\u4fdd\u5b58\u4e34\u65f6\u8ba1\u7b97\u7ed3\u679c\u3002\r\n\tInt k\uff1b\r\n\tInt pc; \/\/\u7a0b\u5e8f\u8ba1\u6570\u5668\uff0c\u7528\u4e8e\u5206\u652f\u8df3\u8f6c\r\n\tFor (pc = 0 ,pc < flen, pc ++){\r\n\t\tFentry = &filter[pc];\r\n\t\tSwitch (fentry->code){\r\n\t\t\tCase BPF_ALU|BPF_ADD|BPF_X:\r\n\t\t\tA += X;\r\n\t\t\tContinue;\r\n\t\t\t..\/\/\u7c7b\u4f3c\u5b9e\u73b0\u51cf\u6cd5\uff0c\u4e58\u6cd5\uff0c\u9664\u6cd5\uff0c\u53d6\u53cd\uff0c\u4e0e\uff0c\u6216\u7b49\u64cd\u4f5c\u3002\r\n\t\t\tCase BPF_JMP|BPF_JA:\/\/\u6d89\u53ca\u5206\u652f\u8df3\u8f6c\r\n\t\t\tPc += fentry->k;\r\n\t\t\tContinue;\r\n\t\t\tCase BPF_JMP|BPF_JGT|BPF_K:\/\/\u5927\u4e8e\r\n\t\t\tPc += (A->fentry->k)?fentry->jt:fentry->jf;\r\n\t\t\tContinue;\r\n\t\t\t..\/\/\u7c7b\u4f3c\u5b9e\u73b0\u5c0f\u4e8e\uff0c\u7b49\u4e8e\uff0c\u6bd4\u8f83\u64cd\u4f5c\uff0c\u7136\u540e\u5206\u652f\u8df3\u8f6c\r\n\r\n\t\t}\r\n}\r\n\tLoad_w: \/\/\/\u52a0\u8f7d\u64cd\u4f5c\uff0c\u7c7b\u4f3c\u6c47\u7f16mov,\u8fd9\u6837load\u4e5f\u662f\u533a\u5206\u5927\u5c0f\u7684\uff0c\u6bd4\u5982\u662fload\u4e00\u4e2a\u5b57\u8fd8\u662f\u53cc\u5b57\uff0c\u8fd8\u662f\u5b57\u8282\u3002\r\n\t\t\tIf(k >=0 &&(unsigned int)(k+sizeof(u32)) <=len){\r\n\t\t\t\tA = ntohl(*(u32*)&data[k]);\r\n\t\t\t\tContinue;\r\n}\r\n}<\/pre>\n\u00a0 \u00a0 BPF\u7528\u4e8e\u5f88\u591a\u7684\u6293\u5305\u7a0b\u5e8f\uff0c\u5728linux\u4e2d\uff0c\u4e00\u822c\u5185\u6838\u81ea\u52a8\u7f16\u8bd1\u8fdb\u4e86af_packet\u8fd9\u4e2a\u9a71\u52a8\uff0c\u56e0\u6b64\u53ea\u9700\u8981\u5728\u7528\u6237\u6001\u914d\u7f6e\u4e00\u4e2aPACKET\u7684socket\uff0c\u7136\u540e\u5c06filter\u914d\u7f6e\u8fdb\u5185\u6838\u5373\u53ef\uff0c\u4f7f\u7528setsockopt\u7684SO_ATTACH_FILTER \u547d\u4ee4\uff0c\u8fd9\u4e2afilter\u662f\u5728\u7528\u6237\u7a7a\u95f4\u914d\u5236\u7684\uff0c\u6bd4\u5982tcpdump\u5e94\u7528\u7a0b\u5e8f\uff0ctcpdump\u548c\u5185\u6838BPF\u8fc7\u6ee4\u5668\u7684\u5173\u7cfb\u7c7b\u4f3ciptables\u4e0enetfilter\u7684\u5173\u7cfb\uff0c\u53ea\u662fNetfilter\u5b9e\u73b0\u4e86match\/target\u7684\u590d\u5408\u914d\u5408\uff0c\u800cBPF\u7684target\u5219\u53ea\u662f\u9009\u62e9\u662f\u5426\u8981\u4e0e\u4e0d\u8981\u3002<\/p>\n
\u00a0 \u00a0 \u56de\u5230\u4e3b\u9898\u4e0a\u6765\uff0cseccomp-bpf\u5728\u4f7f\u7528BPF\u7684\u65f6\u5019\uff0c\u501f\u9274\u4e86\u5176\u601d\u60f3\u3002
\n\u5927\u91cf\u7684\u7cfb\u7edf\u8c03\u7528\u66b4\u9732\u5728\u7528\u6237\u7a7a\u95f4\uff0c\u5728\u7a0b\u5e8f\u7684\u6574\u4e2a\u751f\u547d\u5468\u671f\u5185\u5e76\u6ca1\u6709\u4f7f\u7528\u3002\u800c\u968f\u7740\u7cfb\u7edf\u8c03\u7528\u7684\u6539\u53d8\u548c\u6210\u719f\uff0cbug\u7684\u53d1\u73b0\u548c\u6839\u9664\uff0c\u4e00\u5957\u53ef\u7528\u7684\u7cfb\u7edf\u8c03\u7528\u662f\u6ee1\u8db3\u7528\u6237\u7a0b\u5e8f\u57fa\u672c\u7684\u8c03\u7528\u3002\u5c06\u53ef\u4ee5\u4ea7\u751f\u51fa\u4e00\u7ec4\u5c3d\u91cf\u5c11\u7684\u7cfb\u7edf\u8c03\u7528\u66b4\u9732\u5728\u7528\u6237\u7a7a\u95f4\u3002\u7cfb\u7edf\u8c03\u7528\u7684\u8fc7\u6ee4\u5c31\u662f\u5728\u5e94\u7528\u7a0b\u5e8f\u7684\u4f7f\u7528\u4e2d\u3002<\/p>\n
Seccomp\u8fc7\u6ee4\u5668\u63d0\u7ed9\u4e86\u4e00\u79cd\u624b\u6bb5\uff0c\u4e3a\u4e00\u4e2a\u8fdb\u7a0b\u8c03\u7528\u7cfb\u7edf\u8c03\u7528\u65f6\u6307\u5b9a\u4e86\u8fc7\u6ee4\u5668\uff0c\u800c\u8fd9\u4e2a\u8fc7\u6ee4\u5668\u5219\u662fBPF\u3002BPF\u4f5c\u4e3asocket\u8fc7\u6ee4\u5668\u4e0d\u540c\u4e4b\u5904\u5219\u662f\u64cd\u4f5c\u5f53\u524d\u7684user_regs_struct\u6570\u636e\u7ed3\u6784\uff0c\u8fd9\u9700\u8981\u9884\u5148\u5b9a\u4e49\u597d\u7cfb\u7edf\u8c03\u7528\u7684ABI\u548c\u5b9a\u4e49\u8fc7\u6ee4\u89c4\u5219\u3002\u4f46\u7cfb\u7edf\u8c03\u7528\u7684\u53c2\u6570\u4fdd\u5b58\u5728\u7528\u6237\u7a7a\u95f4\uff0c\u4f46\u8981\u9a8c\u8bc1\u8be5\u53c2\u6570\u662f\u5426\u5b89\u5168\u662f\u975e\u5e38\u56f0\u96be\u7684\u3002<\/p>\n
\u00a0 \u00a0 Seccomp\u7528\u6237\u65e0\u6cd5\u907f\u514dTOCTOU (time-of-check-time-of-use)\u7cfb\u7edf\u8c03\u7528\u5bf9\u6846\u67b6\u7684\u6ce8\u5165\u5f0f\u653b\u51fb\u3002\u5982\u4e00\u4e2a\u6076\u610f\u8fdb\u7a0b\u53ef\u80fd\u4f1a\u5728\u201c\u53c2\u6570\u88ab\u5b89\u5168\u68c0\u67e5\u201d\u4e4b\u540e\uff0c\u800c\u5728\u5b9e\u9645\u4f7f\u7528\u4e4b\u524d\uff0c\u5c06\u53c2\u6570\u6362\u6389\uff0c\u8fd9\u8fb9\u4f7f\u8282\u6216\u7cfb\u7edf\u8c03\u7528\u65f6\u6240\u4f5c\u7684\u53c2\u6570\u68c0\u67e5\u53d8\u5f97\u6ca1\u6709\u610f\u4e49\u3002\u4f46\u8981\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u4e5f\u4e0d\u80fd\u4ec5\u628a\u76ee\u5149\u76ef\u4f4f\u7cfb\u7edf\u7684\u8c03\u7528\u5165\u53e3\u3002<\/p>\n
\u9488\u5bf9\u7cfb\u7edf\u8c03\u7528\u7684\u8fc7\u6ee4\uff0c\u4e0d\u662f\u4e00\u79cd\u6c99\u7bb1\u7684\u6a21\u5f0f\uff0c\u5176\u66f4\u591a\u7684\u63d0\u4f9b\u4e86\u51cf\u5c11\u5185\u6838\u66b4\u9732\u7684\u8868\u9762\uff0c\u9664\u6b64\u4e4b\u5916\uff0c\u9700\u8981\u548c\u5176\u4ed6\u7684\u89c4\u5219\u548c\u65b9\u6848\u8fdb\u884c\u914d\u5408\u3002
\n\u5f53seccomp\u6a21\u5f0f\u88ab\u6dfb\u52a0\uff0c\u4f46\u5b83\u4eec\u4e0d\u662f\u76f4\u63a5\u8bbe\u7f6e\u8d85\u65f6\u7684\u8fc7\u7a0b\uff0c\u662f\u4e00\u79cd\u65b0\u7684\u6a21\u5f0f\uff0c \u4ec5\u5f53CONFIG_SECCOMP_FILTER\u8bbe\u7f6e\uff0c\u5e76\u7528prctl\u542f\u7528PR_ATTACH_SECCOMP_FILTER\u53c2\u6570\u3002
\n\u4e0eseccomp\u8fc7\u6ee4\u5668\u4ea4\u4e92\u5f0f\u901a\u8fc7prctl\u8c03\u7528\u3002
\nPR_ATTACH_SECCOMP_FILTER ,\u5141\u8bb8\u4e00\u4e2a\u65b0\u7684\u8fc7\u6ee4\u5668\u4f7f\u7528BPF\u7a0b\u5e8f\u7684\u89c4\u8303\uff0cBPF\u7a0b\u5e8f\u5c06\u88ab\u6267\u884cuser_regs_struct\u7ed3\u6784\u7684\u6570\u636e\u3002\u7528\u6cd5\u4e3a<\/p>\n
prctl(PA_ATTACH_SECCOMP_FILTER,prog);<\/pre>\n+#include <asm\/unistd.h>\r\n+#include <linux\/filter.h>\r\n+#include <stdio.h>\r\n+#include <stddef.h>\r\n+#include <sys\/user.h>\r\n+#include <unistd.h>\r\n+\r\n+#define regoffset(_reg) (offsetof(struct user_regs_struct, _reg))\r\n+int install_filter(void)\r\n+{\r\n+\tstruct sock_filter filter[] = {\r\n+\t\t\/* Grab the system call number *\/\r\n\t\t\t\/\/BPF_LD \u5c06\u503c\u62f7\u8d1d\u8fdb\u5bc4\u5b58\u5668(accumulator)\r\n\t\t\t\/\/BPF_W Word BPF_H half Word\r\n\t\t\t\/\/BPF_IND \u53ef\u53d8\u7684\u504f\u79fb \r\n\t\t\t\/\/BPF_ABS \u56fa\u5b9a\u7684\u504f\u79fb\r\n\t\t\t\/\/BPF_k \u5e38\u6570 BPF_A \u7d2f\u52a0\u5668\r\n\t\t\t\/\/BPF_JEQ \u5224\u65ad\u662f\u5426\u76f8\u7b49\r\n\t\/\/#define BPF_STMT(code, k) { (unsigned short)(code), 0, 0, k } \r\n\t\/\/#define BPF_JUMP(code, k, jt, jf) { (unsigned short)(code), jt, jf, k } \r\n\r\n+\t\tBPF_STMT(BPF_LD+BPF_W+BPF_IND, regoffset(orig_eax)),\r\n\t\t\/\/\u7269\u7406\u5934\uff0c\u504f\u79fbregoffset(orig_eax) byte\u540e\uff0c\u6307\u5411type*\u3002\r\n+\t\t\/\/* Jump table for the allowed syscalls *\/\r\n\t\t\/\/\u8fdb\u884c\u6bd4\u8f83\uff0c\u662f\u5426\u4e3aI__NR_rt_sigreturn\u3002 true\u7684\u8bdd 0, false 10\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 10, 0),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 9, 0),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 8, 0),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 7, 0),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 2, 6),\r\n+\r\n+\t\t\/* Check that read is only using stdin. *\/\r\n\r\n+\t\tBPF_STMT(BPF_LD+BPF_W+BPF_IND, regoffset(ebx)),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 3, 4),\r\n+\r\n+\t\t\/* Check that write is only using stdout\/stderr *\/\r\n+\t\tBPF_STMT(BPF_LD+BPF_W+BPF_IND, regoffset(ebx)),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0),\r\n+\t\tBPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 0, 1),\r\n+\r\n+\t\t\/* Put the \"accept\" value in A *\/\r\n+\t\tBPF_STMT(BPF_LD+BPF_W+BPF_LEN, 0),\r\n+\r\n+\t\tBPF_STMT(BPF_RET+BPF_A,0),\r\n+\t};\r\n+\tstruct sock_fprog prog = {\r\n+\t\t.len = (unsigned short)(sizeof(filter)\/sizeof(filter[0])),\r\n+\t\t.filter = filter,\r\n+\t};\r\n+\tif (prctl(36, &prog)) { \r\n\t\t\t\t\/\/ prctl(PA_ATTACH_SECCOMP_FILTER,prog);\r\n\r\n+\t\tperror(\"prctl\");\r\n+\t\treturn 1;\r\n+\t}\r\n+\treturn 0;\r\n+}\r\n+\r\n+#define payload(_c) _c, sizeof(_c)\r\n+int main(int argc, char **argv) {\r\n+\tchar buf[4096];\r\n+\tssize_t bytes = 0;\r\n+\tif (install_filter())\r\n+\t\treturn 1;\r\n+\tsyscall(__NR_write, STDOUT_FILENO, payload(\"OHAI! WHAT IS YOUR NAME? \"));\r\n+\tbytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf));\r\n+\tsyscall(__NR_write, STDOUT_FILENO, payload(\"HELLO, \"));\r\n+\tsyscall(__NR_write, STDOUT_FILENO, buf, bytes);\r\n+\treturn 0;\r\n+}<\/pre>\n","protected":false},"excerpt":{"rendered":"\u00a0 \u00a0 \u00a0 \u00a0 linux3.5\u4ee5\u540elinux\u652f\u6301…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[45,51],"tags":[64,56,63,65],"_links":{"self":[{"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=\/wp\/v2\/posts\/370"}],"collection":[{"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=370"}],"version-history":[{"count":4,"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=\/wp\/v2\/posts\/370\/revisions"}],"predecessor-version":[{"id":375,"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=\/wp\/v2\/posts\/370\/revisions\/375"}],"wp:attachment":[{"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=370"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=370"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.selinuxplus.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=370"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"\"](\"http:\/\/www.selinuxplus.com\/wp-content\/uploads\/2013\/07\/bpf-1.png\" "\\"bpf-1\\"")
<\/a><\/p>\n