Make debug() compile-time- and runtime-configurable, and use it around mount_setattr()

.github/workflows/check.yml

@@ -26,7 +26,7 @@ jobs:
       run: mkdir test-logs
     - name: setup
       run: |
-        meson setup _build -Db_sanitize=address,undefined -Doptimization=2
+        meson setup _build -Db_sanitize=address,undefined -Ddebug_logging=true -Doptimization=2
       env:
         CFLAGS: >-
           -Wp,-D_FORTIFY_SOURCE=2
@@ -38,11 +38,13 @@ jobs:
         ./_build/bwrap --bind / / --tmpfs /tmp true
       env:
         ASAN_OPTIONS: detect_leaks=0
+        DEBUG_INVOCATION: '1'
     - name: test
       run: |
         BWRAP_MUST_WORK=1 meson test -C _build
       env:
         ASAN_OPTIONS: detect_leaks=0
+        DEBUG_INVOCATION: '1'
     - name: Collect overall test logs on failure
       if: failure()
       run: mv _build/meson-logs/testlog.txt test-logs/ || true

bind-mount.c

@@ -473,6 +473,7 @@ mount_setattr_fallback (const char *resolved_dest,
                         char **failing_path)
 {
 #if !USE_MOUNT_SETATTR_FALLBACK
+  debug ("No mount_setattr fallback");
   (void) resolved_dest;
   (void) options;
 
@@ -489,6 +490,12 @@ mount_setattr_fallback (const char *resolved_dest,
   cleanup_mount_tab MountTab mount_tab = NULL;
   int i;
 
+  debug ("Remounting mount table entries (%s %s) on  \"%s\" %s",
+         readonly ? "ro" : "rw",
+         devices ? "dev" : "nodev",
+         resolved_dest,
+         recursive ? "recursively" : "only");
+
   mount_tab = parse_mountinfo (resolved_dest);
   if (mount_tab[0].mountpoint == NULL)
     {
@@ -520,6 +527,7 @@ mount_setattr_fallback (const char *resolved_dest,
     {
       for (i = 1; mount_tab[i].mountpoint != NULL; i++)
         {
+          debug ("Acting on submount %s", mount_tab[i].mountpoint);
           current_flags = mount_tab[i].options;
           new_flags = current_flags | (devices ? 0 : MS_NODEV) | MS_NOSUID | (readonly ? MS_RDONLY : 0);
           if (new_flags != current_flags &&
@@ -548,6 +556,7 @@ mount_setattr_fallback (const char *resolved_dest,
         }
     }
 
+  debug ("-> success");
   return BIND_MOUNT_SUCCESS;
 #endif /* USE_MOUNT_SETATTR_FALLBACK */
 }
@@ -679,6 +688,12 @@ mount_setattr_setup (const char *resolved_dest,
         .attr_set = MOUNT_ATTR_NOSUID,
       };
 
+      debug ("Setting mount attributes (%s %s) on  \"%s\" %s",
+             readonly ? "ro" : "rw",
+             devices ? "dev" : "nodev",
+             resolved_dest,
+             recursive ? "recursively" : "only");
+
       if (!devices)
         attr.attr_set |= MOUNT_ATTR_NODEV;
 
@@ -703,6 +718,7 @@ mount_setattr_setup (const char *resolved_dest,
 
       if (mount_setattr_wrapper (resolved_dest_fd, "", setattr_flags, &attr, sizeof(attr)) == 0)
         {
+          debug ("-> success");
           return BIND_MOUNT_SUCCESS;
         }
       else if (errno != ENOSYS)
@@ -711,6 +727,8 @@ mount_setattr_setup (const char *resolved_dest,
             *failing_path = xstrdup (resolved_dest);
           return BIND_MOUNT_ERROR_MOUNT_SETATTR;
         }
+
+      debug ("-> Falling back");
     }
   /* mount_setattr(2) isn't available, so we'll have to do this the hard way: */
   mount_attr_supported = false;

bubblewrap.c

@@ -2920,6 +2920,11 @@ main (int    argc,
   /* Get the (optional) privileges we need */
   acquire_privs ();
 
+#ifdef BWRAP_DEBUG
+  if (getenv ("DEBUG_INVOCATION") != NULL)
+    bwrap_is_debugging = true;
+#endif
+
   /* Never gain any more privs during exec */
   if (prctl (PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0)
     die_with_error ("prctl(PR_SET_NO_NEW_PRIVS) failed");

meson.build

@@ -87,6 +87,10 @@ if selinux_dep.found()
   endif
 endif
 
+if get_option('debug')
+  cdata.set('BWRAP_DEBUG', 1)
+endif
+
 assume_kernel = get_option('assume_kernel')
 if assume_kernel != ''
   kernel_parts = assume_kernel.split('.')

meson_options.txt

@@ -31,6 +31,12 @@ option(
   description : 'generate man pages',
   value : 'auto',
 )
+option(
+  'debug_logging',
+  type : 'boolean',
+  description : 'Provide debug messages, off-by-default',
+  value : false,
+)
 option(
   'program_prefix',
   type : 'string',

utils.c

@@ -39,6 +39,10 @@
 #define security_check_context(x) security_check_context ((security_context_t) x)
 #endif
 
+#ifdef BWRAP_DEBUG
+bool bwrap_is_debugging = false;
+#endif
+
 bool bwrap_level_prefix = false;
 int proc_fd = -1;
 
@@ -48,6 +52,9 @@ bwrap_logv (int severity,
             va_list args,
             const char *detail)
 {
+  if (severity == LOG_DEBUG && !bwrap_is_debugging)
+    return;
+
   if (bwrap_level_prefix)
     fprintf (stderr, "<%d>", severity);
 

utils.h

@@ -33,7 +33,8 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#if 0
+#ifdef BWRAP_DEBUG
+extern bool bwrap_is_debugging;
 #define debug(...) bwrap_log (LOG_DEBUG, __VA_ARGS__)
 #else
 #define debug(...)