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 #if HAVE_SECCOMP
  26 #include <seccomp.h>
  27 #endif
  28
  29 #include "alloc-util.h"
  30 #include "log.h"
  31 #include "nspawn-seccomp.h"
  32 #if HAVE_SECCOMP
  33 #include "seccomp-util.h"
  34 #endif
  35 #include "string-util.h"
  36 #include "strv.h"
  37
  38 #if HAVE_SECCOMP
  39
  40 static int seccomp_add_default_syscall_filter(
  41                 scmp_filter_ctx ctx,
  42                 uint32_t arch,
  43                 uint64_t cap_list_retain,
  44                 char **syscall_whitelist,
  45                 char **syscall_blacklist) {
  46
  47         static const struct {
  48                 uint64_t capability;
  49                 const char* name;
  50         } whitelist[] = {
  51                 /* Let's use set names where we can */
  52                 { 0,                  "@aio"                   },
  53                 { 0,                  "@basic-io"              },
  54                 { 0,                  "@chown"                 },
  55                 { 0,                  "@default"               },
  56                 { 0,                  "@file-system"           },
  57                 { 0,                  "@io-event"              },
  58                 { 0,                  "@ipc"                   },
  59                 { 0,                  "@mount"                 },
  60                 { 0,                  "@network-io"            },
  61                 { 0,                  "@process"               },
  62                 { 0,                  "@resources"             },
  63                 { 0,                  "@setuid"                },
  64                 { 0,                  "@signal"                },
  65                 { 0,                  "@sync"                  },
  66                 { 0,                  "@timer"                 },
  67
  68                 /* The following four are sets we optionally enable, in case the caps have been configured for it */
  69                 { CAP_SYS_TIME,       "@clock"                 },
  70                 { CAP_SYS_MODULE,     "@module"                },
  71                 { CAP_SYS_RAWIO,      "@raw-io"                },
  72                 { CAP_IPC_LOCK,       "@memlock"               },
  73
  74                 /* Plus a good set of additional syscalls which are not part of any of the groups above */
  75                 { 0,                  "brk"                    },
  76                 { 0,                  "capget"                 },
  77                 { 0,                  "capset"                 },
  78                 { 0,                  "copy_file_range"        },
  79                 { 0,                  "fadvise64"              },
  80                 { 0,                  "fadvise64_64"           },
  81                 { 0,                  "flock"                  },
  82                 { 0,                  "get_mempolicy"          },
  83                 { 0,                  "getcpu"                 },
  84                 { 0,                  "getpriority"            },
  85                 { 0,                  "getrandom"              },
  86                 { 0,                  "ioctl"                  },
  87                 { 0,                  "ioprio_get"             },
  88                 { 0,                  "kcmp"                   },
  89                 { 0,                  "madvise"                },
  90                 { 0,                  "mincore"                },
  91                 { 0,                  "mprotect"               },
  92                 { 0,                  "mremap"                 },
  93                 { 0,                  "name_to_handle_at"      },
  94                 { 0,                  "oldolduname"            },
  95                 { 0,                  "olduname"               },
  96                 { 0,                  "personality"            },
  97                 { 0,                  "readahead"              },
  98                 { 0,                  "readdir"                },
  99                 { 0,                  "remap_file_pages"       },
 100                 { 0,                  "sched_get_priority_max" },
 101                 { 0,                  "sched_get_priority_min" },
 102                 { 0,                  "sched_getaffinity"      },
 103                 { 0,                  "sched_getattr"          },
 104                 { 0,                  "sched_getparam"         },
 105                 { 0,                  "sched_getscheduler"     },
 106                 { 0,                  "sched_rr_get_interval"  },
 107                 { 0,                  "sched_yield"            },
 108                 { 0,                  "seccomp"                },
 109                 { 0,                  "sendfile"               },
 110                 { 0,                  "sendfile64"             },
 111                 { 0,                  "setdomainname"          },
 112                 { 0,                  "setfsgid"               },
 113                 { 0,                  "setfsgid32"             },
 114                 { 0,                  "setfsuid"               },
 115                 { 0,                  "setfsuid32"             },
 116                 { 0,                  "sethostname"            },
 117                 { 0,                  "setpgid"                },
 118                 { 0,                  "setsid"                 },
 119                 { 0,                  "splice"                 },
 120                 { 0,                  "sysinfo"                },
 121                 { 0,                  "tee"                    },
 122                 { 0,                  "umask"                  },
 123                 { 0,                  "uname"                  },
 124                 { 0,                  "userfaultfd"            },
 125                 { 0,                  "vmsplice"               },
 126
 127                 /* The following individual syscalls are added depending on specified caps */
 128                 { CAP_SYS_PACCT,      "acct"                   },
 129                 { CAP_SYS_PTRACE,     "process_vm_readv"       },
 130                 { CAP_SYS_PTRACE,     "process_vm_writev"      },
 131                 { CAP_SYS_PTRACE,     "ptrace"                 },
 132                 { CAP_SYS_BOOT,       "reboot"                 },
 133                 { CAP_SYSLOG,         "syslog"                 },
 134                 { CAP_SYS_TTY_CONFIG, "vhangup"                },
 135
 136                 /*
 137                  * The following syscalls and groups are knowingly excluded:
 138                  *
 139                  * @cpu-emulation
 140                  * @keyring           (NB: keyring is not namespaced!)
 141                  * @obsolete
 142                  * @swap
 143                  *
 144                  * bpf                (NB: bpffs is not namespaced!)
 145                  * fanotify_init
 146                  * fanotify_mark
 147                  * kexec_file_load
 148                  * kexec_load
 149                  * lookup_dcookie
 150                  * nfsservctl
 151                  * open_by_handle_at
 152                  * perf_event_open
 153                  * pkey_alloc
 154                  * pkey_free
 155                  * pkey_mprotect
 156                  * quotactl
 157                  */
 158         };
 159
 160         int r, c = 0;
 161         size_t i;
 162         char **p;
 163
 164         for (i = 0; i < ELEMENTSOF(whitelist); i++) {
 165                 if (whitelist[i].capability != 0 && (cap_list_retain & (1ULL << whitelist[i].capability)) == 0)
 166                         continue;
 167
 168                 r = seccomp_add_syscall_filter_item(ctx, whitelist[i].name, SCMP_ACT_ALLOW, syscall_blacklist);
 169                 if (r < 0)
 170                         /* If the system call is not known on this architecture, then that's fine, let's ignore it */
 171                         log_debug_errno(r, "Failed to add rule for system call %s on %s, ignoring: %m", whitelist[i].name, seccomp_arch_to_string(arch));
 172                 else
 173                         c++;
 174         }
 175
 176         STRV_FOREACH(p, syscall_whitelist) {
 177                 r = seccomp_add_syscall_filter_item(ctx, *p, SCMP_ACT_ALLOW, syscall_blacklist);
 178                 if (r < 0)
 179                         log_debug_errno(r, "Failed to add rule for system call %s on %s, ignoring: %m", *p, seccomp_arch_to_string(arch));
 180                 else
 181                         c++;
 182         }
 183
 184         return c;
 185 }
 186
 187 int setup_seccomp(uint64_t cap_list_retain, char **syscall_whitelist, char **syscall_blacklist) {
 188         uint32_t arch;
 189         int r;
 190
 191         if (!is_seccomp_available()) {
 192                 log_debug("SECCOMP features not detected in the kernel, disabling SECCOMP filterering");
 193                 return 0;
 194         }
 195
 196         SECCOMP_FOREACH_LOCAL_ARCH(arch) {
 197                 _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
 198
 199                 log_debug("Applying whitelist on architecture: %s", seccomp_arch_to_string(arch));
 200
 201                 r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ERRNO(EPERM));
 202                 if (r < 0)
 203                         return log_error_errno(r, "Failed to allocate seccomp object: %m");
 204
 205                 r = seccomp_add_default_syscall_filter(seccomp, arch, cap_list_retain, syscall_whitelist, syscall_blacklist);
 206                 if (r < 0)
 207                         return r;
 208
 209                 r = seccomp_load(seccomp);
 210                 if (IN_SET(r, -EPERM, -EACCES))
 211                         return log_error_errno(r, "Failed to install seccomp filter: %m");
 212                 if (r < 0)
 213                         log_debug_errno(r, "Failed to install filter set for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
 214         }
 215
 216         SECCOMP_FOREACH_LOCAL_ARCH(arch) {
 217                 _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
 218
 219                 log_debug("Applying NETLINK_AUDIT mask on architecture: %s", seccomp_arch_to_string(arch));
 220
 221                 r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
 222                 if (r < 0)
 223                         return log_error_errno(r, "Failed to allocate seccomp object: %m");
 224
 225                 /*
 226                   Audit is broken in containers, much of the userspace audit hookup will fail if running inside a
 227                   container. We don't care and just turn off creation of audit sockets.
 228
 229                   This will make socket(AF_NETLINK, *, NETLINK_AUDIT) fail with EAFNOSUPPORT which audit userspace uses
 230                   as indication that audit is disabled in the kernel.
 231                 */
 232
 233                 r = seccomp_rule_add_exact(
 234                                 seccomp,
 235                                 SCMP_ACT_ERRNO(EAFNOSUPPORT),
 236                                 SCMP_SYS(socket),
 237                                 2,
 238                                 SCMP_A0(SCMP_CMP_EQ, AF_NETLINK),
 239                                 SCMP_A2(SCMP_CMP_EQ, NETLINK_AUDIT));
 240                 if (r < 0) {
 241                         log_debug_errno(r, "Failed to add audit seccomp rule, ignoring: %m");
 242                         continue;
 243                 }
 244
 245                 r = seccomp_load(seccomp);
 246                 if (IN_SET(r, -EPERM, -EACCES))
 247                         return log_error_errno(r, "Failed to install seccomp audit filter: %m");
 248                 if (r < 0)
 249                         log_debug_errno(r, "Failed to install filter set for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
 250         }
 251
 252         return 0;
 253 }
 254
 255 #else
 256
 257 int setup_seccomp(uint64_t cap_list_retain, char **syscall_whitelist, char **syscall_blacklist) {
 258         return 0;
 259 }
 260
 261 #endif