Support /proc in _dbus_file_get_content

procfs has special semantics: most files are 0 size,
only one read can be done on a file, and they are
not larger than 4MB. Enhance _dbus_file_get_content()
so that we can read files from /proc with it.

Signed-off-by: Luca Boccassi <bluca@debian.org>

5 files changed, 64 insertions, 4 deletions

diff --git a/cmake/ConfigureChecks.cmake b/cmake/ConfigureChecks.cmake
index 172db213..dfa21a55 100644
--- a/cmake/ConfigureChecks.cmake
+++ b/cmake/ConfigureChecks.cmake
@@ -15,6 +15,7 @@ check_include_file(errno.h     HAVE_ERRNO_H)    # dbus-sysdeps.c
 check_include_file(inttypes.h     HAVE_INTTYPES_H)   # dbus-pipe.h
 check_include_file(io.h         HAVE_IO_H)      # internal
 check_include_file(linux/close_range.h HAVE_LINUX_CLOSE_RANGE_H)
+check_include_file(linux/magic.h HAVE_LINUX_MAGIC_H)
 check_include_file(locale.h     HAVE_LOCALE_H)
 check_include_file(signal.h     HAVE_SIGNAL_H)
 check_include_file(stdio.h      HAVE_STDIO_H)   # dbus-sysdeps.h
@@ -26,6 +27,7 @@ check_include_file(sys/resource.h     HAVE_SYS_RESOURCE_H)
 check_include_file(sys/syscall.h HAVE_SYS_SYSCALL_H)
 check_include_file(sys/prctl.h  HAVE_SYS_PRCTL_H)
 check_include_file(sys/time.h   HAVE_SYS_TIME_H)# dbus-sysdeps-win.c
+check_include_file(sys/vfs.h    HAVE_SYS_VFS_H)
 check_include_file(ws2tcpip.h   HAVE_WS2TCPIP_H)# dbus-sysdeps-win.c
 check_include_file(unistd.h     HAVE_UNISTD_H)  # dbus-sysdeps-util-win.c
 check_include_file(sys/inotify.h DBUS_BUS_ENABLE_INOTIFY)
@@ -64,6 +66,7 @@ check_symbol_exists(environ      "unistd.h"                  HAVE_DECL_ENVIRON)
 check_symbol_exists(LOG_PERROR   "syslog.h"                  HAVE_DECL_LOG_PERROR)
 check_symbol_exists(setresuid    "unistd.h"                  HAVE_SETRESUID)
 check_symbol_exists(getresuid    "unistd.h"                  HAVE_GETRESUID)
+check_symbol_exists(fstatfs      "sys/vfs.h"                 HAVE_FSTATFS)
 
 check_struct_member(cmsgcred cmcred_pid "sys/types.h;sys/socket.h" HAVE_CMSGCRED)   #  dbus-sysdeps.c
 
diff --git a/cmake/config.h.cmake b/cmake/config.h.cmake
index 395a583d..43771b99 100644
--- a/cmake/config.h.cmake
+++ b/cmake/config.h.cmake
@@ -120,10 +120,12 @@
 #cmakedefine HAVE_SYSLOG_H 1
 #cmakedefine HAVE_SYS_EVENTS_H 1
 #cmakedefine HAVE_SYS_INOTIFY_H 1
+#cmakedefine HAVE_LINUX_MAGIC_H 1
 #cmakedefine HAVE_SYS_PRCTL_H 1
 #cmakedefine HAVE_SYS_RANDOM_H 1
 #cmakedefine HAVE_SYS_RESOURCE_H 1
 #cmakedefine HAVE_SYS_SYSCALL_H 1
+#cmakedefine HAVE_SYS_VFS_H 1
 
 /* Define to 1 if you have sys/time.h */
 #cmakedefine    HAVE_SYS_TIME_H 1
@@ -185,6 +187,7 @@
 
 #cmakedefine HAVE_ACCEPT4 1
 
+#cmakedefine HAVE_FSTATFS 1
 #cmakedefine HAVE_INOTIFY_INIT1 1
 #cmakedefine HAVE_GETRANDOM 1
 #cmakedefine HAVE_GETRLIMIT 1
diff --git a/configure.ac b/configure.ac
index 92124838..2620f372 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1023,6 +1023,9 @@ if test x$with_valgrind != xno; then
   AC_DEFINE([WITH_VALGRIND], [1], [Define to add Valgrind instrumentation])
 fi
 
+AC_CHECK_HEADERS(sys/vfs.h, [AC_CHECK_FUNCS(fstatfs)])
+AC_CHECK_HEADERS([linux/magic.h])
+
 #### Set up final flags
 LIBDBUS_LIBS="$THREAD_LIBS $NETWORK_libs $SYSTEMD_LIBS"
 AC_SUBST([LIBDBUS_LIBS])
diff --git a/dbus/dbus-file-unix.c b/dbus/dbus-file-unix.c
index 6da44504..d5fa029e 100644
--- a/dbus/dbus-file-unix.c
+++ b/dbus/dbus-file-unix.c
@@ -33,7 +33,13 @@
 #include "dbus-sysdeps.h"
 #include "dbus-sysdeps-unix.h"
 
+#ifdef HAVE_LINUX_MAGIC_H
+#include <linux/magic.h>
+#endif
 #include <sys/stat.h>
+#ifdef HAVE_SYS_VFS_H
+#include <sys/vfs.h>
+#endif
 #include <stdio.h>
 #include <fcntl.h>
 #include <unistd.h>
@@ -60,9 +66,14 @@ _dbus_file_get_contents (DBusString       *str,
 {
   int fd;
   struct stat sb;
+#ifdef HAVE_FSTATFS
+  struct statfs sfs;
+#endif
   int orig_len;
   int total;
+  int file_size;
   const char *filename_c;
+  dbus_bool_t is_procfs = FALSE;
 
   _DBUS_ASSERT_ERROR_IS_CLEAR (error);
   
@@ -104,17 +115,47 @@ _dbus_file_get_contents (DBusString       *str,
       _dbus_close (fd, NULL);
       return FALSE;
     }
+
+  /* procfs has different semantics - most files are 0 size,
+   * we can do only one read, and at most we can read 4M.
+   */
+#ifdef HAVE_FSTATFS
+  if (sb.st_size == 0)
+    {
+      if (fstatfs(fd, &sfs) < 0)
+        {
+          dbus_set_error (error, _dbus_error_from_errno (errno),
+                          "Failed to stat \"%s\": %s",
+                          filename_c,
+                          _dbus_strerror (errno));
+
+          _dbus_verbose ("fstatvfs() failed: %s",
+                        _dbus_strerror (errno));
+
+          _dbus_close (fd, NULL);
+
+          return FALSE;
+        }
+      if (sfs.f_type == PROC_SUPER_MAGIC)
+        is_procfs = TRUE;
+    }
+#endif
+
+  if (is_procfs)
+    file_size = _DBUS_ONE_MEGABYTE;
+  else
+    file_size = sb.st_size;
   
   total = 0;
   orig_len = _dbus_string_get_length (str);
-  if (sb.st_size > 0 && S_ISREG (sb.st_mode))
+  if (file_size > 0 && S_ISREG (sb.st_mode))
     {
       int bytes_read;
 
-      while (total < (int) sb.st_size)
+      do
         {
           bytes_read = _dbus_read (fd, str,
-                                   sb.st_size - total);
+                                   file_size - total);
           if (bytes_read <= 0)
             {
               dbus_set_error (error, _dbus_error_from_errno (errno),
@@ -132,11 +173,12 @@ _dbus_file_get_contents (DBusString       *str,
           else
             total += bytes_read;
         }
+      while (total < file_size && !is_procfs);
 
       _dbus_close (fd, NULL);
       return TRUE;
     }
-  else if (sb.st_size != 0)
+  else if (file_size != 0)
     {
       _dbus_verbose ("Can only open regular files at the moment.\n");
       dbus_set_error (error, DBUS_ERROR_FAILED,
diff --git a/meson.build b/meson.build
index df302a7d..e2cbc368 100644
--- a/meson.build
+++ b/meson.build
@@ -670,6 +670,7 @@ check_headers = [
     'io.h',
     'locale.h',
     'linux/close_range.h',
+    'linux/magic.h',
     'locale.h',
     'signal.h',
     'syslog.h',
@@ -678,6 +679,7 @@ check_headers = [
     'sys/resource.h',
     'sys/syscall.h',
     'sys/time.h',
+    'sys/vfs.h',
     'unistd.h',
     'ws2tcpip.h',
 ]
@@ -753,6 +755,13 @@ config.set('HAVE_UNPCBID',
     )
 )
 
+config.set('HAVE_FSTATFS',
+    cc.has_function(
+        'fstatfs',
+        prefix : '#include <sys/vfs.h>',
+        args: compile_args_c,
+    )
+)
 
 ###############################################################################
 # Project options