src/nspawn/nspawn-seccomp.c

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