Merge pull request #509 from tomsmeding/tmpfs-size

Add --size option to control size of a --tmpfs

bubblewrap.c

@@ -23,6 +23,7 @@
 #include <sched.h>
 #include <pwd.h>
 #include <grp.h>
+#include <ctype.h>
 #include <sys/mount.h>
 #include <sys/socket.h>
 #include <sys/wait.h>
@@ -52,6 +53,12 @@
        __result; }))
 #endif
 
+/* We limit the size of a tmpfs to half the architecture's address space,
+ * to avoid hitting arbitrary limits in the kernel.
+ * For example, on at least one x86_64 machine, the actual limit seems to be
+ * 2^64 - 2^12. */
+#define MAX_TMPFS_BYTES ((size_t) (SIZE_MAX >> 1))
+
 /* Globals to avoid having to use getuid(), since the uid/gid changes during runtime */
 static uid_t real_uid;
 static gid_t real_gid;
@@ -91,6 +98,7 @@ int opt_userns_fd = -1;
 int opt_userns2_fd = -1;
 int opt_pidns_fd = -1;
 int next_perms = -1;
+size_t next_size_arg = 0;
 
 #define CAP_TO_MASK_0(x) (1L << ((x) & 31))
 #define CAP_TO_MASK_1(x) CAP_TO_MASK_0(x - 32)
@@ -149,6 +157,7 @@ struct _SetupOp
   int         fd;
   SetupOpFlag flags;
   int         perms;
+  size_t      size;  /* number of bytes, zero means unset/default */
   SetupOp    *next;
 };
 
@@ -177,6 +186,7 @@ typedef struct
   uint32_t op;
   uint32_t flags;
   uint32_t perms;
+  size_t   size_arg;
   uint32_t arg1_offset;
   uint32_t arg2_offset;
 } PrivSepOp;
@@ -341,6 +351,7 @@ usage (int ecode, FILE *out)
            "    --cap-add CAP                Add cap CAP when running as privileged user\n"
            "    --cap-drop CAP               Drop cap CAP when running as privileged user\n"
            "    --perms OCTAL                Set permissions of next argument (--bind-data, --file, etc.)\n"
+           "    --size BYTES                 Set size of next argument (only for --tmpfs)\n"
            "    --chmod OCTAL PATH           Change permissions of PATH (must already exist)\n"
           );
   exit (ecode);
@@ -1001,6 +1012,7 @@ privileged_op (int         privileged_op_socket,
                uint32_t    op,
                uint32_t    flags,
                uint32_t    perms,
+               size_t      size_arg,
                const char *arg1,
                const char *arg2)
 {
@@ -1033,6 +1045,7 @@ privileged_op (int         privileged_op_socket,
       op_buffer->op = op;
       op_buffer->flags = flags;
       op_buffer->perms = perms;
+      op_buffer->size_arg = size_arg;
       op_buffer->arg1_offset = arg1_offset;
       op_buffer->arg2_offset = arg2_offset;
       if (arg1 != NULL)
@@ -1099,7 +1112,18 @@ privileged_op (int         privileged_op_socket,
 
     case PRIV_SEP_OP_TMPFS_MOUNT:
       {
-        cleanup_free char *mode = xasprintf ("mode=%#o", perms);
+        cleanup_free char *mode = NULL;
+
+        /* This check should be unnecessary since we checked this when parsing
+         * the --size option as well. However, better be safe than sorry. */
+        if (size_arg > MAX_TMPFS_BYTES)
+          die_with_error ("Specified tmpfs size too large (%zu > %zu)", size_arg, MAX_TMPFS_BYTES);
+
+        if (size_arg != 0)
+          mode = xasprintf ("mode=%#o,size=%zu", perms, size_arg);
+        else
+          mode = xasprintf ("mode=%#o", perms);
+
         cleanup_free char *opt = label_mount (mode, opt_file_label);
         if (mount ("tmpfs", arg1, "tmpfs", MS_NOSUID | MS_NODEV, opt) != 0)
           die_with_error ("Can't mount tmpfs on %s", arg1);
@@ -1200,12 +1224,12 @@ setup_newroot (bool unshare_pid,
                          PRIV_SEP_OP_BIND_MOUNT,
                          (op->type == SETUP_RO_BIND_MOUNT ? BIND_READONLY : 0) |
                          (op->type == SETUP_DEV_BIND_MOUNT ? BIND_DEVICES : 0),
-                         0, source, dest);
+                         0, 0, source, dest);
           break;
 
         case SETUP_REMOUNT_RO_NO_RECURSIVE:
           privileged_op (privileged_op_socket,
-                         PRIV_SEP_OP_REMOUNT_RO_NO_RECURSIVE, 0, 0, NULL, dest);
+                         PRIV_SEP_OP_REMOUNT_RO_NO_RECURSIVE, 0, 0, 0, NULL, dest);
           break;
 
         case SETUP_MOUNT_PROC:
@@ -1216,14 +1240,14 @@ setup_newroot (bool unshare_pid,
             {
               /* Our own procfs */
               privileged_op (privileged_op_socket,
-                             PRIV_SEP_OP_PROC_MOUNT, 0, 0,
+                             PRIV_SEP_OP_PROC_MOUNT, 0, 0, 0,
                              dest, NULL);
             }
           else
             {
               /* Use system procfs, as we share pid namespace anyway */
               privileged_op (privileged_op_socket,
-                             PRIV_SEP_OP_BIND_MOUNT, 0, 0,
+                             PRIV_SEP_OP_BIND_MOUNT, 0, 0, 0,
                              "oldroot/proc", dest);
             }
 
@@ -1245,7 +1269,7 @@ setup_newroot (bool unshare_pid,
                 }
 
               privileged_op (privileged_op_socket,
-                             PRIV_SEP_OP_BIND_MOUNT, BIND_READONLY, 0,
+                             PRIV_SEP_OP_BIND_MOUNT, BIND_READONLY, 0, 0,
                              subdir, subdir);
             }
 
@@ -1256,7 +1280,7 @@ setup_newroot (bool unshare_pid,
             die_with_error ("Can't mkdir %s", op->dest);
 
           privileged_op (privileged_op_socket,
-                         PRIV_SEP_OP_TMPFS_MOUNT, 0, 0755,
+                         PRIV_SEP_OP_TMPFS_MOUNT, 0, 0755, 0,
                          dest, NULL);
 
           static const char *const devnodes[] = { "null", "zero", "full", "random", "urandom", "tty" };
@@ -1267,7 +1291,7 @@ setup_newroot (bool unshare_pid,
               if (create_file (node_dest, 0444, NULL) != 0)
                 die_with_error ("Can't create file %s/%s", op->dest, devnodes[i]);
               privileged_op (privileged_op_socket,
-                             PRIV_SEP_OP_BIND_MOUNT, BIND_DEVICES, 0,
+                             PRIV_SEP_OP_BIND_MOUNT, BIND_DEVICES, 0, 0,
                              node_src, node_dest);
             }
 
@@ -1301,7 +1325,7 @@ setup_newroot (bool unshare_pid,
             if (mkdir (pts, 0755) == -1)
               die_with_error ("Can't create %s/devpts", op->dest);
             privileged_op (privileged_op_socket,
-                           PRIV_SEP_OP_DEVPTS_MOUNT, 0, 0, pts, NULL);
+                           PRIV_SEP_OP_DEVPTS_MOUNT, 0, 0, 0, pts, NULL);
 
             if (symlink ("pts/ptmx", ptmx) != 0)
               die_with_error ("Can't make symlink at %s/ptmx", op->dest);
@@ -1321,7 +1345,7 @@ setup_newroot (bool unshare_pid,
                 die_with_error ("creating %s/console", op->dest);
 
               privileged_op (privileged_op_socket,
-                             PRIV_SEP_OP_BIND_MOUNT, BIND_DEVICES, 0,
+                             PRIV_SEP_OP_BIND_MOUNT, BIND_DEVICES, 0, 0,
                              src_tty_dev, dest_console);
             }
 
@@ -1336,7 +1360,7 @@ setup_newroot (bool unshare_pid,
             die_with_error ("Can't mkdir %s", op->dest);
 
           privileged_op (privileged_op_socket,
-                         PRIV_SEP_OP_TMPFS_MOUNT, 0, op->perms,
+                         PRIV_SEP_OP_TMPFS_MOUNT, 0, op->perms, op->size,
                          dest, NULL);
           break;
 
@@ -1345,7 +1369,7 @@ setup_newroot (bool unshare_pid,
             die_with_error ("Can't mkdir %s", op->dest);
 
           privileged_op (privileged_op_socket,
-                         PRIV_SEP_OP_MQUEUE_MOUNT, 0, 0,
+                         PRIV_SEP_OP_MQUEUE_MOUNT, 0, 0, 0,
                          dest, NULL);
           break;
 
@@ -1426,7 +1450,7 @@ setup_newroot (bool unshare_pid,
             privileged_op (privileged_op_socket,
                            PRIV_SEP_OP_BIND_MOUNT,
                            (op->type == SETUP_MAKE_RO_BIND_FILE ? BIND_READONLY : 0),
-                           0, tempfile, dest);
+                           0, 0, tempfile, dest);
 
             /* Remove the file so we're sure the app can't get to it in any other way.
                Its outside the container chroot, so it shouldn't be possible, but lets
@@ -1444,7 +1468,7 @@ setup_newroot (bool unshare_pid,
         case SETUP_SET_HOSTNAME:
           assert (op->dest != NULL);  /* guaranteed by the constructor */
           privileged_op (privileged_op_socket,
-                         PRIV_SEP_OP_SET_HOSTNAME, 0, 0,
+                         PRIV_SEP_OP_SET_HOSTNAME, 0, 0, 0,
                          op->dest, NULL);
           break;
 
@@ -1453,7 +1477,7 @@ setup_newroot (bool unshare_pid,
         }
     }
   privileged_op (privileged_op_socket,
-                 PRIV_SEP_OP_DONE, 0, 0, NULL, NULL);
+                 PRIV_SEP_OP_DONE, 0, 0, 0, NULL, NULL);
 }
 
 /* Do not leak file descriptors already used by setup_newroot () */
@@ -1540,6 +1564,7 @@ read_priv_sec_op (int          read_socket,
                   size_t       buffer_size,
                   uint32_t    *flags,
                   uint32_t    *perms,
+                  size_t      *size_arg,
                   const char **arg1,
                   const char **arg2)
 {
@@ -1564,6 +1589,7 @@ read_priv_sec_op (int          read_socket,
 
   *flags = op->flags;
   *perms = op->perms;
+  *size_arg = op->size_arg;
   *arg1 = resolve_string_offset (buffer, rec_len, op->arg1_offset);
   *arg2 = resolve_string_offset (buffer, rec_len, op->arg2_offset);
 
@@ -1578,25 +1604,10 @@ print_version_and_exit (void)
 }
 
 static int
-takes_perms (const char *next_option)
+is_modifier_option (const char *option)
 {
-  static const char *const options_that_take_perms[] =
+  return strcmp (option, "--perms") == 0
-  {
+         || strcmp(option, "--size") == 0;
-    "--bind-data",
-    "--dir",
-    "--file",
-    "--ro-bind-data",
-    "--tmpfs",
-  };
-  size_t i;
-
-  for (i = 0; i < N_ELEMENTS (options_that_take_perms); i++)
-    {
-      if (strcmp (options_that_take_perms[i], next_option) == 0)
-        return 1;
-    }
-
-  return 0;
 }
 
 static void
@@ -1633,9 +1644,6 @@ parse_args_recurse (int          *argcp,
     {
       const char *arg = argv[0];
 
-      if (next_perms >= 0 && !takes_perms (arg))
-        die ("--perms must be followed by an option that creates a file");
-
       if (strcmp (arg, "--help") == 0)
         {
           usage (EXIT_SUCCESS, stdout);
@@ -1893,6 +1901,13 @@ parse_args_recurse (int          *argcp,
             op->perms = 0755;
 
           next_perms = -1;
+
+          /* If the option is unset, next_size_arg is zero, which results in
+           * the default tmpfs size. This is exactly what we want. */
+          op->size = next_size_arg;
+
+          next_size_arg = 0;
+
           argv += 1;
           argc -= 1;
         }
@@ -2386,6 +2401,9 @@ parse_args_recurse (int          *argcp,
           if (argc < 2)
             die ("--perms takes an argument");
 
+          if (next_perms != -1)
+            die ("--perms given twice for the same action");
+
           perms = strtoul (argv[1], &endptr, 8);
 
           if (argv[1][0] == '\0'
@@ -2396,6 +2414,42 @@ parse_args_recurse (int          *argcp,
 
           next_perms = (int) perms;
 
+          argv += 1;
+          argc -= 1;
+        }
+      else if (strcmp (arg, "--size") == 0)
+        {
+          unsigned long long size;
+          char *endptr = NULL;
+
+          if (is_privileged)
+            die ("The --size option is not permitted in setuid mode");
+
+          if (argc < 2)
+            die ("--size takes an argument");
+
+          if (next_size_arg != 0)
+            die ("--size given twice for the same action");
+
+          errno = 0;  /* reset errno so we can detect ERANGE from strtoull */
+
+          size = strtoull (argv[1], &endptr, 0);
+
+          /* isdigit: Not only check that the first digit is not '\0', but
+           * simultaneously guard against negative numbers or preceding
+           * spaces. */
+          if (errno != 0  /* from strtoull */
+              || !isdigit(argv[1][0])
+              || endptr == NULL
+              || *endptr != '\0'
+              || size == 0)
+            die ("--size takes a non-zero number of bytes");
+
+          if (size > MAX_TMPFS_BYTES)
+            die ("--size (for tmpfs) is limited to %zu", MAX_TMPFS_BYTES);
+
+          next_size_arg = (size_t) size;
+
           argv += 1;
           argc -= 1;
         }
@@ -2438,6 +2492,16 @@ parse_args_recurse (int          *argcp,
           break;
         }
 
+      /* If --perms was set for the current action but the current action
+       * didn't consume the setting, apparently --perms wasn't suitable for
+       * this action. */
+      if (!is_modifier_option(arg) && next_perms >= 0)
+        die ("--perms must be followed by an option that creates a file");
+
+      /* Similarly for --size. */
+      if (!is_modifier_option(arg) && next_size_arg != 0)
+        die ("--size must be followed by --tmpfs");
+
       argv++;
       argc--;
     }
@@ -3022,6 +3086,7 @@ main (int    argc,
           int status;
           uint32_t buffer[2048];  /* 8k, but is int32 to guarantee nice alignment */
           uint32_t op, flags, perms;
+          size_t size_arg;
           const char *arg1, *arg2;
           cleanup_fd int unpriv_socket = -1;
 
@@ -3031,8 +3096,8 @@ main (int    argc,
           do
             {
               op = read_priv_sec_op (unpriv_socket, buffer, sizeof (buffer),
-                                     &flags, &perms, &arg1, &arg2);
+                                     &flags, &perms, &size_arg, &arg1, &arg2);
-              privileged_op (-1, op, flags, perms, arg1, arg2);
+              privileged_op (-1, op, flags, perms, size_arg, arg1, arg2);
               if (write (unpriv_socket, buffer, 1) != 1)
                 die ("Can't write to op_socket");
             }

bwrap.xml

@@ -207,6 +207,9 @@
     (rwxr-xr-x). However, if a <option>--perms</option> option is in effect, and
     it sets the permissions for group or other to zero, then newly-created
     parent directories will also have their corresponding permission set to zero.
+    <option>--size</option> modifies the size of the created mount when preceding a
+    <option>--tmpfs</option> action; <option>--perms</option> and <option>--size</option>
+    can be combined.
   </para>
   <variablelist>
     <varlistentry>
@@ -217,7 +220,24 @@
         Subsequent operations are not affected: for example,
         <literal>--perms 0700 --tmpfs /a --tmpfs /b</literal> will mount
         <filename>/a</filename> with permissions 0700, then return to
-        the default permissions for <filename>/b</filename>.</para></listitem>
+        the default permissions for <filename>/b</filename>.
+        Note that <option>--perms</option> and <option>--size</option> can be
+        combined: <literal>--perms 0700 --size 10485760 --tmpfs /s</literal> will apply
+        permissions as well as a maximum size to the created tmpfs.</para></listitem>
+    </varlistentry>
+    <varlistentry>
+      <term><option>--size <arg choice="plain">BYTES</arg></option></term>
+      <listitem><para>This option does nothing on its own, and must be followed
+        by <literal>--tmpfs</literal>. It sets the size in bytes for the next tmpfs.
+        For example, <literal>--size 10485760 --tmpfs /tmp</literal> will create a tmpfs
+        at <filename>/tmp</filename> of size 10MiB. Subsequent operations are not
+        affected: for example,
+        <literal>--size 10485760 --tmpfs /a --tmpfs /b</literal> will mount
+        <filename>/a</filename> with size 10MiB, then return to the default size for
+        <filename>/b</filename>.
+        Note that <option>--perms</option> and <option>--size</option> can be
+        combined: <literal>--size 10485760 --perms 0700 --tmpfs /s</literal> will apply
+        permissions as well as a maximum size to the created tmpfs.</para></listitem>
     </varlistentry>
     <varlistentry>
       <term><option>--bind <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
@@ -260,7 +280,9 @@
       <listitem>
         <para>Mount new tmpfs on <arg choice="plain">DEST</arg>.
           If the previous option was <option>--perms</option>, it sets the
-          mode of the tmpfs. Otherwise, the tmpfs has mode 0755.</para>
+          mode of the tmpfs. Otherwise, the tmpfs has mode 0755.
+          If the previous option was <option>--size</option>, it sets the
+          size in bytes of the tmpfs. Otherwise, the tmpfs has the default size.</para>
       </listitem>
     </varlistentry>
     <varlistentry>

completions/bash/bwrap

@@ -54,6 +54,7 @@ _bwrap() {
 		--ro-bind
 		--seccomp
 		--setenv
+		--size
 		--symlink
 		--sync-fd
 		--uid

completions/zsh/_bwrap

@@ -1,11 +1,23 @@
 #compdef bwrap
 
+_bwrap_args_after_perms_size=(
+    # Please sort alphabetically (in LC_ALL=C order) by option name
+    '--tmpfs[Mount new tmpfs on DEST]:mount point for tmpfs:_files -/'
+)
+
 _bwrap_args_after_perms=(
     # Please sort alphabetically (in LC_ALL=C order) by option name
     '--bind-data[Copy from FD to file which is bind-mounted on DEST]: :_guard "[0-9]#" "file descriptor to read content":destination:_files'
     '--dir[Create dir at DEST]:directory to create:_files -/'
     '--file[Copy from FD to destination DEST]: :_guard "[0-9]#" "file descriptor to read content from":destination:_files'
     '--ro-bind-data[Copy from FD to file which is readonly bind-mounted on DEST]: :_guard "[0-9]#" "file descriptor to read content from":destination:_files'
+    '--size[Set size in bytes for next action argument]: :->after_perms_size'
+    '--tmpfs[Mount new tmpfs on DEST]:mount point for tmpfs:_files -/'
+)
+
+_bwrap_args_after_size=(
+    # Please sort alphabetically (in LC_ALL=C order) by option name
+    '--perms[Set permissions for next action argument]: :_guard "[0-7]#" "permissions in octal": :->after_perms_size'
     '--tmpfs[Mount new tmpfs on DEST]:mount point for tmpfs:_files -/'
 )
 
@@ -47,6 +59,7 @@ _bwrap_args=(
     '--ro-bind[Bind mount the host path SRC readonly on DEST]:source:_files:destination:_files'
     '--seccomp[Load and use seccomp rules from FD]: :_guard "[0-9]#" "file descriptor to read seccomp rules from"'
     '--setenv[Set an environment variable]:variable to set:_parameters -g "*export*":value of variable: :'
+    '--size[Set size in bytes for next action argument]: :->after_size'
     '--symlink[Create symlink at DEST with target SRC]:symlink target:_files:symlink to create:_files:'
     '--sync-fd[Keep this fd open while sandbox is running]: :_guard "[0-9]#" "file descriptor to keep open"'
     '--uid[Custom uid in the sandbox (requires --unshare-user or --userns)]: :_guard "[0-9]#" "numeric group ID"'
@@ -73,6 +86,14 @@ _bwrap() {
             _values -S ' ' 'option' $_bwrap_args_after_perms
             ;;
 
+        after_size)
+            _values -S ' ' 'option' $_bwrap_args_after_size
+            ;;
+
+        after_perms_size)
+            _values -S ' ' 'option' $_bwrap_args_after_perms_size
+            ;;
+
         caps)
             # $ grep -E '#define\sCAP_\w+\s+[0-9]+' /usr/include/linux/capability.h | awk '{print $2}' | xargs echo
             local all_caps=(

tests/test-run.sh

@@ -8,7 +8,7 @@ srcd=$(cd $(dirname "$0") && pwd)
 
 bn=$(basename "$0")
 
-echo "1..54"
+echo "1..57"
 
 # Test help
 ${BWRAP} --help > help.txt
@@ -405,6 +405,29 @@ $RUN \
 assert_file_has_content dir-permissions '^755$'
 echo "ok - tmpfs has expected permissions"
 
+# 1048576 = 1 MiB
+$RUN \
+    --size 1048576 --tmpfs "$(pwd -P)" \
+    df --output=size --block-size=1K "$(pwd -P)" > dir-size
+assert_file_has_content dir-size '^ *1024$'
+$RUN \
+    --size 1048576 --perms 01777 --tmpfs "$(pwd -P)" \
+    stat -c '%a' "$(pwd -P)" > dir-permissions
+assert_file_has_content dir-permissions '^1777$'
+$RUN \
+    --size 1048576 --perms 01777 --tmpfs "$(pwd -P)" \
+    df --output=size --block-size=1K "$(pwd -P)" > dir-size
+assert_file_has_content dir-size '^ *1024$'
+$RUN \
+    --perms 01777 --size 1048576 --tmpfs "$(pwd -P)" \
+    stat -c '%a' "$(pwd -P)" > dir-permissions
+assert_file_has_content dir-permissions '^1777$'
+$RUN \
+    --perms 01777 --size 1048576 --tmpfs "$(pwd -P)" \
+    df --output=size --block-size=1K "$(pwd -P)" > dir-size
+assert_file_has_content dir-size '^ *1024$'
+echo "ok - tmpfs has expected size"
+
 $RUN \
     --file 0 /tmp/file \
     stat -c '%a' /tmp/file < /dev/null > file-permissions
@@ -431,6 +454,40 @@ $RUN \
 assert_file_has_content file-permissions '^640$'
 echo "ok - files have expected permissions"
 
+if $RUN --size 0 --tmpfs /tmp/a true; then
+    assert_not_reached Zero tmpfs size allowed
+fi
+if $RUN --size 123bogus --tmpfs /tmp/a true; then
+    assert_not_reached Bogus tmpfs size allowed
+fi
+if $RUN --size '' --tmpfs /tmp/a true; then
+    assert_not_reached Empty tmpfs size allowed
+fi
+if $RUN --size -12345678 --tmpfs /tmp/a true; then
+    assert_not_reached Negative tmpfs size allowed
+fi
+if $RUN --size ' -12345678' --tmpfs /tmp/a true; then
+    assert_not_reached Negative tmpfs size with space allowed
+fi
+# This is 2^64
+if $RUN --size 18446744073709551616 --tmpfs /tmp/a true; then
+    assert_not_reached Overflowing tmpfs size allowed
+fi
+# This is 2^63 + 1; note that the current max size is SIZE_MAX/2
+if $RUN --size 9223372036854775809 --tmpfs /tmp/a true; then
+    assert_not_reached Too-large tmpfs size allowed
+fi
+echo "ok - bogus tmpfs size not allowed"
+
+if $RUN --perms 0640 --perms 0640 --tmpfs /tmp/a true; then
+    assert_not_reached Multiple perms options allowed
+fi
+if $RUN --size 1048576 --size 1048576 --tmpfs /tmp/a true; then
+    assert_not_reached Multiple perms options allowed
+fi
+echo "ok - --perms and --size only allowed once"
+
+
 FOO= BAR=baz $RUN --setenv FOO bar sh -c 'echo "$FOO$BAR"' > stdout
 assert_file_has_content stdout barbaz
 FOO=wrong BAR=baz $RUN --setenv FOO bar sh -c 'echo "$FOO$BAR"' > stdout