src/nspawn/nspawn-seccomp.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   Copyright 2016 Lennart Poettering
   4 ***/
   5
   6 #include <errno.h>
   7 #include <linux/netlink.h>
   8 #include <sys/capability.h>
   9 #include <sys/types.h>
  10
  11 #if HAVE_SECCOMP
  12 #include <seccomp.h>
  13 #endif
  14
  15 #include "alloc-util.h"
  16 #include "log.h"
  17 #include "nspawn-seccomp.h"
  18 #if HAVE_SECCOMP
  19 #include "seccomp-util.h"
  20 #endif
  21 #include "string-util.h"
  22 #include "strv.h"
  23
  24 #if HAVE_SECCOMP
  25
  26 static int seccomp_add_default_syscall_filter(
  27                 scmp_filter_ctx ctx,
  28                 uint32_t arch,
  29                 uint64_t cap_list_retain,
  30                 char **syscall_whitelist,
  31                 char **syscall_blacklist) {
  32
  33         static const struct {
  34                 uint64_t capability;
  35                 const char* name;
  36         } whitelist[] = {
  37                 /* Let's use set names where we can */
  38                 { 0,                  "@aio"                   },
  39                 { 0,                  "@basic-io"              },
  40                 { 0,                  "@chown"                 },
  41                 { 0,                  "@default"               },
  42                 { 0,                  "@file-system"           },
  43                 { 0,                  "@io-event"              },
  44                 { 0,                  "@ipc"                   },
  45                 { 0,                  "@mount"                 },
  46                 { 0,                  "@network-io"            },
  47                 { 0,                  "@process"               },
  48                 { 0,                  "@resources"             },
  49                 { 0,                  "@setuid"                },
  50                 { 0,                  "@signal"                },
  51                 { 0,                  "@sync"                  },
  52                 { 0,                  "@timer"                 },
  53
  54                 /* The following four are sets we optionally enable, in case the caps have been configured for it */
  55                 { CAP_SYS_TIME,       "@clock"                 },
  56                 { CAP_SYS_MODULE,     "@module"                },
  57                 { CAP_SYS_RAWIO,      "@raw-io"                },
  58                 { CAP_IPC_LOCK,       "@memlock"               },
  59
  60                 /* Plus a good set of additional syscalls which are not part of any of the groups above */
  61                 { 0,                  "brk"                    },
  62                 { 0,                  "capget"                 },
  63                 { 0,                  "capset"                 },
  64                 { 0,                  "copy_file_range"        },
  65                 { 0,                  "fadvise64"              },
  66                 { 0,                  "fadvise64_64"           },
  67                 { 0,                  "flock"                  },
  68                 { 0,                  "get_mempolicy"          },
  69                 { 0,                  "getcpu"                 },
  70                 { 0,                  "getpriority"            },
  71                 { 0,                  "getrandom"              },
  72                 { 0,                  "ioctl"                  },
  73                 { 0,                  "ioprio_get"             },
  74                 { 0,                  "kcmp"                   },
  75                 { 0,                  "madvise"                },
  76                 { 0,                  "mincore"                },
  77                 { 0,                  "mprotect"               },
  78                 { 0,                  "mremap"                 },
  79                 { 0,                  "name_to_handle_at"      },
  80                 { 0,                  "oldolduname"            },
  81                 { 0,                  "olduname"               },
  82                 { 0,                  "personality"            },
  83                 { 0,                  "readahead"              },
  84                 { 0,                  "readdir"                },
  85                 { 0,                  "remap_file_pages"       },
  86                 { 0,                  "sched_get_priority_max" },
  87                 { 0,                  "sched_get_priority_min" },
  88                 { 0,                  "sched_getaffinity"      },
  89                 { 0,                  "sched_getattr"          },
  90                 { 0,                  "sched_getparam"         },
  91                 { 0,                  "sched_getscheduler"     },
  92                 { 0,                  "sched_rr_get_interval"  },
  93                 { 0,                  "sched_yield"            },
  94                 { 0,                  "seccomp"                },
  95                 { 0,                  "sendfile"               },
  96                 { 0,                  "sendfile64"             },
  97                 { 0,                  "setdomainname"          },
  98                 { 0,                  "setfsgid"               },
  99                 { 0,                  "setfsgid32"             },
 100                 { 0,                  "setfsuid"               },
 101                 { 0,                  "setfsuid32"             },
 102                 { 0,                  "sethostname"            },
 103                 { 0,                  "setpgid"                },
 104                 { 0,                  "setsid"                 },
 105                 { 0,                  "splice"                 },
 106                 { 0,                  "sysinfo"                },
 107                 { 0,                  "tee"                    },
 108                 { 0,                  "umask"                  },
 109                 { 0,                  "uname"                  },
 110                 { 0,                  "userfaultfd"            },
 111                 { 0,                  "vmsplice"               },
 112
 113                 /* The following individual syscalls are added depending on specified caps */
 114                 { CAP_SYS_PACCT,      "acct"                   },
 115                 { CAP_SYS_PTRACE,     "process_vm_readv"       },
 116                 { CAP_SYS_PTRACE,     "process_vm_writev"      },
 117                 { CAP_SYS_PTRACE,     "ptrace"                 },
 118                 { CAP_SYS_BOOT,       "reboot"                 },
 119                 { CAP_SYSLOG,         "syslog"                 },
 120                 { CAP_SYS_TTY_CONFIG, "vhangup"                },
 121
 122                 /*
 123                  * The following syscalls and groups are knowingly excluded:
 124                  *
 125                  * @cpu-emulation
 126                  * @keyring           (NB: keyring is not namespaced!)
 127                  * @obsolete
 128                  * @swap
 129                  *
 130                  * bpf                (NB: bpffs is not namespaced!)
 131                  * fanotify_init
 132                  * fanotify_mark
 133                  * kexec_file_load
 134                  * kexec_load
 135                  * lookup_dcookie
 136                  * nfsservctl
 137                  * open_by_handle_at
 138                  * perf_event_open
 139                  * pkey_alloc
 140                  * pkey_free
 141                  * pkey_mprotect
 142                  * quotactl
 143                  */
 144         };
 145
 146         int r, c = 0;
 147         size_t i;
 148         char **p;
 149
 150         for (i = 0; i < ELEMENTSOF(whitelist); i++) {
 151                 if (whitelist[i].capability != 0 && (cap_list_retain & (1ULL << whitelist[i].capability)) == 0)
 152                         continue;
 153
 154                 r = seccomp_add_syscall_filter_item(ctx, whitelist[i].name, SCMP_ACT_ALLOW, syscall_blacklist);
 155                 if (r < 0)
 156                         /* If the system call is not known on this architecture, then that's fine, let's ignore it */
 157                         log_debug_errno(r, "Failed to add rule for system call %s on %s, ignoring: %m", whitelist[i].name, seccomp_arch_to_string(arch));
 158                 else
 159                         c++;
 160         }
 161
 162         STRV_FOREACH(p, syscall_whitelist) {
 163                 r = seccomp_add_syscall_filter_item(ctx, *p, SCMP_ACT_ALLOW, syscall_blacklist);
 164                 if (r < 0)
 165                         log_debug_errno(r, "Failed to add rule for system call %s on %s, ignoring: %m", *p, seccomp_arch_to_string(arch));
 166                 else
 167                         c++;
 168         }
 169
 170         return c;
 171 }
 172
 173 int setup_seccomp(uint64_t cap_list_retain, char **syscall_whitelist, char **syscall_blacklist) {
 174         uint32_t arch;
 175         int r;
 176
 177         if (!is_seccomp_available()) {
 178                 log_debug("SECCOMP features not detected in the kernel, disabling SECCOMP filterering");
 179                 return 0;
 180         }
 181
 182         SECCOMP_FOREACH_LOCAL_ARCH(arch) {
 183                 _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
 184
 185                 log_debug("Applying whitelist on architecture: %s", seccomp_arch_to_string(arch));
 186
 187                 r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ERRNO(EPERM));
 188                 if (r < 0)
 189                         return log_error_errno(r, "Failed to allocate seccomp object: %m");
 190
 191                 r = seccomp_add_default_syscall_filter(seccomp, arch, cap_list_retain, syscall_whitelist, syscall_blacklist);
 192                 if (r < 0)
 193                         return r;
 194
 195                 r = seccomp_load(seccomp);
 196                 if (IN_SET(r, -EPERM, -EACCES))
 197                         return log_error_errno(r, "Failed to install seccomp filter: %m");
 198                 if (r < 0)
 199                         log_debug_errno(r, "Failed to install filter set for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
 200         }
 201
 202         SECCOMP_FOREACH_LOCAL_ARCH(arch) {
 203                 _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
 204
 205                 log_debug("Applying NETLINK_AUDIT mask on architecture: %s", seccomp_arch_to_string(arch));
 206
 207                 r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
 208                 if (r < 0)
 209                         return log_error_errno(r, "Failed to allocate seccomp object: %m");
 210
 211                 /*
 212                   Audit is broken in containers, much of the userspace audit hookup will fail if running inside a
 213                   container. We don't care and just turn off creation of audit sockets.
 214
 215                   This will make socket(AF_NETLINK, *, NETLINK_AUDIT) fail with EAFNOSUPPORT which audit userspace uses
 216                   as indication that audit is disabled in the kernel.
 217                 */
 218
 219                 r = seccomp_rule_add_exact(
 220                                 seccomp,
 221                                 SCMP_ACT_ERRNO(EAFNOSUPPORT),
 222                                 SCMP_SYS(socket),
 223                                 2,
 224                                 SCMP_A0(SCMP_CMP_EQ, AF_NETLINK),
 225                                 SCMP_A2(SCMP_CMP_EQ, NETLINK_AUDIT));
 226                 if (r < 0) {
 227                         log_debug_errno(r, "Failed to add audit seccomp rule, ignoring: %m");
 228                         continue;
 229                 }
 230
 231                 r = seccomp_load(seccomp);
 232                 if (IN_SET(r, -EPERM, -EACCES))
 233                         return log_error_errno(r, "Failed to install seccomp audit filter: %m");
 234                 if (r < 0)
 235                         log_debug_errno(r, "Failed to install filter set for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
 236         }
 237
 238         return 0;
 239 }
 240
 241 #else
 242
 243 int setup_seccomp(uint64_t cap_list_retain, char **syscall_whitelist, char **syscall_blacklist) {
 244         return 0;
 245 }
 246
 247 #endif