c - seccomp —如何进行EXIT_SUCCESS？

设置严格模式seccomp后，请转到EXIT_SUCCESS。在main的末尾调用syscall(SYS_exit, EXIT_SUCCESS);是正确的做法吗？

#include <stdlib.h>
#include <unistd.h>
#include <sys/prctl.h>
#include <linux/seccomp.h>
#include <sys/syscall.h>

int main(int argc, char **argv) {
  prctl(PR_SET_SECCOMP, SECCOMP_MODE_STRICT);

  //return EXIT_SUCCESS; // does not work
  //_exit(EXIT_SUCCESS); // does not work
  // syscall(__NR_exit, EXIT_SUCCESS); // (EDIT) This works! Is this the ultimate answer and the right way to exit success from seccomp-ed programs?
  syscall(SYS_exit, EXIT_SUCCESS); // (EDIT) works; SYS_exit equals __NR_exit
}

// gcc seccomp.c -o seccomp && ./seccomp; echo "${?}" # I want 0

最佳答案

如eigenstate.org和SECCOMP (2)中所述:

结果，人们希望_exit()能够正常工作，但这是一个包装函数，它调用严格模式([1]， [2])中不允许的exit_group(2)，因此该进程被终止。

甚至在exit(2) - Linux man page中也有报道:

return语句也会发生同样的情况，它最终会以与_exit()相似的方式终止进程。

跟踪该过程将提供进一步的确认(要显示出来，您不必设置PR_SET_SECCOMP；只需注释prctl())，并且对于两种无效情况，我都得到类似的输出:

linux12:/home/users/grad1459>gcc seccomp.c -o seccomp
linux12:/home/users/grad1459>strace ./seccomp
execve("./seccomp", ["./seccomp"], [/* 24 vars */]) = 0
brk(0)                                  = 0x8784000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb775f000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=97472, ...}) = 0
mmap2(NULL, 97472, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7747000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220\226\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1730024, ...}) = 0
mmap2(NULL, 1739484, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xdd0000
mmap2(0xf73000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a3) = 0xf73000
mmap2(0xf76000, 10972, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xf76000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7746000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7746900, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xf73000, 8192, PROT_READ)     = 0
mprotect(0x8049000, 4096, PROT_READ)    = 0
mprotect(0x16e000, 4096, PROT_READ)     = 0
munmap(0xb7747000, 97472)               = 0
exit_group(0)                           = ?
linux12:/home/users/grad1459>

如您所见，exit_group()被调用，解释了一切!

现在，正如您正确说的那样，“SYS_exit equals __NR_exit”；例如，它在mit.syscall.h中定义:

#define SYS_exit __NR_exit

因此最后两个调用是等效的，即您可以使用自己喜欢的一个，输出应为:

linux12:/home/users/grad1459>gcc seccomp.c -o seccomp && ./seccomp ; echo "${?}"
0

聚苯乙烯

您当然可以自己定义一个filter并使用:

prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, filter);

如本征状态链接中所述，允许_exit()(或严格来说是exit_group(2))，但只有在您确实需要并且知道自己在做什么时才这样做。

关于c - seccomp —如何进行EXIT_SUCCESS？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/33150281/