kernel/seccomp.c

   1 /*
   2  * linux/kernel/seccomp.c
   3  *
   4  * Copyright 2004-2005  Andrea Arcangeli <andrea@cpushare.com>
   5  *
   6  * This defines a simple but solid secure-computing mode.
   7  */
   8
   9 #include <linux/audit.h>
  10 #include <linux/seccomp.h>
  11 #include <linux/sched.h>
  12 #include <linux/compat.h>
  13
  14 /* #define SECCOMP_DEBUG 1 */
  15 #define NR_SECCOMP_MODES 1
  16
  17 /*
  18  * Secure computing mode 1 allows only read/write/exit/sigreturn.
  19  * To be fully secure this must be combined with rlimit
  20  * to limit the stack allocations too.
  21  */
  22 static int mode1_syscalls[] = {
  23         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
  24         0, /* null terminated */
  25 };
  26
  27 #ifdef CONFIG_COMPAT
  28 static int mode1_syscalls_32[] = {
  29         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
  30         0, /* null terminated */
  31 };
  32 #endif
  33
  34 void __secure_computing(int this_syscall)
  35 {
  36         int mode = current->seccomp.mode;
  37         int * syscall;
  38
  39         switch (mode) {
  40         case 1:
  41                 syscall = mode1_syscalls;
  42 #ifdef CONFIG_COMPAT
  43                 if (is_compat_task())
  44                         syscall = mode1_syscalls_32;
  45 #endif
  46                 do {
  47                         if (*syscall == this_syscall)
  48                                 return;
  49                 } while (*++syscall);
  50                 break;
  51         default:
  52                 BUG();
  53         }
  54
  55 #ifdef SECCOMP_DEBUG
  56         dump_stack();
  57 #endif
  58         audit_seccomp(this_syscall);
  59         do_exit(SIGKILL);
  60 }
  61
  62 long prctl_get_seccomp(void)
  63 {
  64         return current->seccomp.mode;
  65 }
  66
  67 long prctl_set_seccomp(unsigned long seccomp_mode)
  68 {
  69         long ret;
  70
  71         /* can set it only once to be even more secure */
  72         ret = -EPERM;
  73         if (unlikely(current->seccomp.mode))
  74                 goto out;
  75
  76         ret = -EINVAL;
  77         if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
  78                 current->seccomp.mode = seccomp_mode;
  79                 set_thread_flag(TIF_SECCOMP);
  80 #ifdef TIF_NOTSC
  81                 disable_TSC();
  82 #endif
  83                 ret = 0;
  84         }
  85
  86  out:
  87         return ret;
  88 }