src/nspawn/nspawn-seccomp.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2016 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <linux/netlink.h>
  22 #include <sys/capability.h>
  23 #include <sys/types.h>
  24
  25 #ifdef HAVE_SECCOMP
  26 #include <seccomp.h>
  27 #endif
  28
  29 #include "alloc-util.h"
  30 #include "log.h"
  31 #include "nspawn-seccomp.h"
  32 #ifdef HAVE_SECCOMP
  33 #include "seccomp-util.h"
  34 #endif
  35 #include "string-util.h"
  36
  37 #ifdef HAVE_SECCOMP
  38
  39 static int seccomp_add_default_syscall_filter(
  40                 scmp_filter_ctx ctx,
  41                 uint32_t arch,
  42                 uint64_t cap_list_retain) {
  43
  44         static const struct {
  45                 uint64_t capability;
  46                 const char* name;
  47         } blacklist[] = {
  48                 { 0,              "@obsolete"           },
  49                 { 0,              "@keyring"            }, /* keyring is not namespaced */
  50                 { 0,              "bpf"                 },
  51                 { 0,              "kexec_file_load"     },
  52                 { 0,              "kexec_load"          },
  53                 { 0,              "lookup_dcookie"      },
  54                 { 0,              "open_by_handle_at"   },
  55                 { 0,              "perf_event_open"     },
  56                 { 0,              "quotactl"            },
  57                 { 0,              "@swap"               },
  58                 { CAP_SYSLOG,     "syslog"              },
  59                 { CAP_SYS_MODULE, "@module"             },
  60                 { CAP_SYS_PACCT,  "acct"                },
  61                 { CAP_SYS_PTRACE, "process_vm_readv"    },
  62                 { CAP_SYS_PTRACE, "process_vm_writev"   },
  63                 { CAP_SYS_PTRACE, "ptrace"              },
  64                 { CAP_SYS_RAWIO,  "@raw-io"             },
  65                 { CAP_SYS_TIME,   "@clock"              },
  66         };
  67
  68         int r, c = 0;
  69         size_t i;
  70
  71         for (i = 0; i < ELEMENTSOF(blacklist); i++) {
  72                 if (blacklist[i].capability != 0 && (cap_list_retain & (1ULL << blacklist[i].capability)))
  73                         continue;
  74
  75                 r = seccomp_add_syscall_filter_item(ctx, blacklist[i].name, SCMP_ACT_ERRNO(EPERM));
  76                 if (r < 0)
  77                         /* If the system call is not known on this architecture, then that's fine, let's ignore it */
  78                         log_debug_errno(r, "Failed to add rule for system call %s, ignoring: %m", blacklist[i].name);
  79                 else
  80                         c++;
  81         }
  82
  83         return c;
  84 }
  85
  86 int setup_seccomp(uint64_t cap_list_retain) {
  87         uint32_t arch;
  88         int r;
  89
  90         if (!is_seccomp_available()) {
  91                 log_debug("SECCOMP features not detected in the kernel, disabling SECCOMP audit filter");
  92                 return 0;
  93         }
  94
  95         SECCOMP_FOREACH_LOCAL_ARCH(arch) {
  96                 _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
  97                 int n;
  98
  99                 log_debug("Operating on architecture: %s", seccomp_arch_to_string(arch));
 100
 101                 r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
 102                 if (r < 0)
 103                         return log_error_errno(r, "Failed to allocate seccomp object: %m");
 104
 105                 n = seccomp_add_default_syscall_filter(seccomp, arch, cap_list_retain);
 106                 if (n < 0)
 107                         return n;
 108
 109                 /*
 110                   Audit is broken in containers, much of the userspace audit hookup will fail if running inside a
 111                   container. We don't care and just turn off creation of audit sockets.
 112
 113                   This will make socket(AF_NETLINK, *, NETLINK_AUDIT) fail with EAFNOSUPPORT which audit userspace uses
 114                   as indication that audit is disabled in the kernel.
 115                 */
 116
 117                 r = seccomp_rule_add_exact(
 118                                 seccomp,
 119                                 SCMP_ACT_ERRNO(EAFNOSUPPORT),
 120                                 SCMP_SYS(socket),
 121                                 2,
 122                                 SCMP_A0(SCMP_CMP_EQ, AF_NETLINK),
 123                                 SCMP_A2(SCMP_CMP_EQ, NETLINK_AUDIT));
 124                 if (r < 0)
 125                         log_debug_errno(r, "Failed to add audit seccomp rule, ignoring: %m");
 126                 else
 127                         n++;
 128
 129                 if (n <= 0) /* no rule added? then skip this architecture */
 130                         continue;
 131
 132                 r = seccomp_load(seccomp);
 133                 if (IN_SET(r, -EPERM, -EACCES))
 134                         return log_error_errno(r, "Failed to install seccomp audit filter: %m");
 135                 if (r < 0)
 136                         log_debug_errno(r, "Failed to install filter set for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
 137         }
 138
 139         return 0;
 140 }
 141
 142 #else
 143
 144 int setup_seccomp(uint64_t cap_list_retain) {
 145         return 0;
 146 }
 147
 148 #endif