From 8fef6abe1131da0c8a7211c740a12ebe11cbcc51 Mon Sep 17 00:00:00 2001
From: Philip Withnall <pwithnall@endlessos.org>
Date: Wed, 10 Mar 2021 16:05:55 +0000
Subject: [PATCH 1/3] glocalfileoutputstream: Factor out a flag check
This clarifies the code a little. It introduces no functional changes.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
---
gio/glocalfileoutputstream.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/gio/glocalfileoutputstream.c b/gio/glocalfileoutputstream.c
index 57d2d5dfe..6a70b2a04 100644
--- a/gio/glocalfileoutputstream.c
+++ b/gio/glocalfileoutputstream.c
@@ -751,6 +751,7 @@ handle_overwrite_open (const char *filename,
int res;
int mode;
int errsv;
+ gboolean replace_destination_set = (flags & G_FILE_CREATE_REPLACE_DESTINATION);
mode = mode_from_flags_or_info (flags, reference_info);
@@ -857,8 +858,8 @@ handle_overwrite_open (const char *filename,
* The second strategy consist simply in copying the old file
* to a backup file and rewrite the contents of the file.
*/
-
- if ((flags & G_FILE_CREATE_REPLACE_DESTINATION) ||
+
+ if (replace_destination_set ||
(!(original_stat.st_nlink > 1) && !is_symlink))
{
char *dirname, *tmp_filename;
@@ -877,7 +878,7 @@ handle_overwrite_open (const char *filename,
/* try to keep permissions (unless replacing) */
- if ( ! (flags & G_FILE_CREATE_REPLACE_DESTINATION) &&
+ if (!replace_destination_set &&
(
#ifdef HAVE_FCHOWN
fchown (tmpfd, original_stat.st_uid, original_stat.st_gid) == -1 ||
@@ -1016,7 +1017,7 @@ handle_overwrite_open (const char *filename,
}
}
- if (flags & G_FILE_CREATE_REPLACE_DESTINATION)
+ if (replace_destination_set)
{
g_close (fd, NULL);
--
2.31.1
From 6c10e8ce6905e8fcc3466eb8af707b5d0d3bdb85 Mon Sep 17 00:00:00 2001
From: Philip Withnall <pwithnall@endlessos.org>
Date: Wed, 24 Feb 2021 17:36:07 +0000
Subject: [PATCH 2/3] glocalfileoutputstream: Fix CREATE_REPLACE_DESTINATION
with symlinks
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
The `G_FILE_CREATE_REPLACE_DESTINATION` flag is equivalent to unlinking
the destination file and re-creating it from scratch. That did
previously work, but in the process the code would call `open(O_CREAT)`
on the file. If the file was a dangling symlink, this would create the
destination file (empty). That’s not an intended side-effect, and has
security implications if the symlink is controlled by a lower-privileged
process.
Fix that by not opening the destination file if it’s a symlink, and
adjusting the rest of the code to cope with
- the fact that `fd == -1` is not an error iff `is_symlink` is true,
- and that `original_stat` will contain the `lstat()` results for the
symlink now, rather than the `stat()` results for its target (again,
iff `is_symlink` is true).
This means that the target of the dangling symlink is no longer created,
which was the bug. The symlink itself continues to be replaced (as
before) with the new file — this is the intended behaviour of
`g_file_replace()`.
The behaviour for non-symlink cases, or cases where the symlink was not
dangling, should be unchanged.
Includes a unit test.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Fixes: #2325
---
gio/glocalfileoutputstream.c | 63 ++++++++++++++-------
gio/tests/file.c | 107 ++++++++++++++++++++++++++++++++++-
2 files changed, 149 insertions(+), 21 deletions(-)
diff --git a/gio/glocalfileoutputstream.c b/gio/glocalfileoutputstream.c
index 6a70b2a04..4a7766f68 100644
--- a/gio/glocalfileoutputstream.c
+++ b/gio/glocalfileoutputstream.c
@@ -779,16 +779,22 @@ handle_overwrite_open (const char *filename,
/* Could be a symlink, or it could be a regular ELOOP error,
* but then the next open will fail too. */
is_symlink = TRUE;
- fd = g_open (filename, open_flags, mode);
+ if (!replace_destination_set)
+ fd = g_open (filename, open_flags, mode);
}
-#else
- fd = g_open (filename, open_flags, mode);
- errsv = errno;
+#else /* if !O_NOFOLLOW */
/* This is racy, but we do it as soon as possible to minimize the race */
is_symlink = g_file_test (filename, G_FILE_TEST_IS_SYMLINK);
+
+ if (!is_symlink || !replace_destination_set)
+ {
+ fd = g_open (filename, open_flags, mode);
+ errsv = errno;
+ }
#endif
- if (fd == -1)
+ if (fd == -1 &&
+ (!is_symlink || !replace_destination_set))
{
char *display_name = g_filename_display_name (filename);
g_set_error (error, G_IO_ERROR,
@@ -800,10 +806,17 @@ handle_overwrite_open (const char *filename,
}
#ifdef G_OS_WIN32
- res = GLIB_PRIVATE_CALL (g_win32_fstat) (fd, &original_stat);
-#else
- res = fstat (fd, &original_stat);
+#error This patch has not been ported to Windows, sorry
#endif
+
+ if (!is_symlink)
+ {
+ res = fstat (fd, &original_stat);
+ }
+ else
+ {
+ res = lstat (filename, &original_stat);
+ }
errsv = errno;
if (res != 0)
@@ -821,16 +834,27 @@ handle_overwrite_open (const char *filename,
if (!S_ISREG (original_stat.st_mode))
{
if (S_ISDIR (original_stat.st_mode))
- g_set_error_literal (error,
- G_IO_ERROR,
- G_IO_ERROR_IS_DIRECTORY,
- _("Target file is a directory"));
- else
- g_set_error_literal (error,
- G_IO_ERROR,
- G_IO_ERROR_NOT_REGULAR_FILE,
- _("Target file is not a regular file"));
- goto err_out;
+ {
+ g_set_error_literal (error,
+ G_IO_ERROR,
+ G_IO_ERROR_IS_DIRECTORY,
+ _("Target file is a directory"));
+ goto err_out;
+ }
+ else if (!is_symlink ||
+#ifdef S_ISLNK
+ !S_ISLNK (original_stat.st_mode)
+#else
+ FALSE
+#endif
+ )
+ {
+ g_set_error_literal (error,
+ G_IO_ERROR,
+ G_IO_ERROR_NOT_REGULAR_FILE,
+ _("Target file is not a regular file"));
+ goto err_out;
+ }
}
if (etag != NULL)
@@ -911,7 +935,8 @@ handle_overwrite_open (const char *filename,
}
}
- g_close (fd, NULL);
+ if (fd >= 0)
+ g_close (fd, NULL);
*temp_filename = tmp_filename;
return tmpfd;
}
diff --git a/gio/tests/file.c b/gio/tests/file.c
index 98eeb85d4..44db6e295 100644
--- a/gio/tests/file.c
+++ b/gio/tests/file.c
@@ -671,8 +671,6 @@ test_replace_cancel (void)
guint count;
GError *error = NULL;
- g_test_bug ("629301");
-
path = g_dir_make_tmp ("g_file_replace_cancel_XXXXXX", &error);
g_assert_no_error (error);
tmpdir = g_file_new_for_path (path);
@@ -779,6 +777,110 @@ test_replace_cancel (void)
g_object_unref (tmpdir);
}
+static void
+test_replace_symlink (void)
+{
+#ifdef G_OS_UNIX
+ gchar *tmpdir_path = NULL;
+ GFile *tmpdir = NULL, *source_file = NULL, *target_file = NULL;
+ GFileOutputStream *stream = NULL;
+ const gchar *new_contents = "this is a test message which should be written to source and not target";
+ gsize n_written;
+ GFileEnumerator *enumerator = NULL;
+ GFileInfo *info = NULL;
+ gchar *contents = NULL;
+ gsize length = 0;
+ GError *local_error = NULL;
+
+ /* Create a fresh, empty working directory. */
+ tmpdir_path = g_dir_make_tmp ("g_file_replace_symlink_XXXXXX", &local_error);
+ g_assert_no_error (local_error);
+ tmpdir = g_file_new_for_path (tmpdir_path);
+
+ g_test_message ("Using temporary directory %s", tmpdir_path);
+ g_free (tmpdir_path);
+
+ /* Create symlink `source` which points to `target`. */
+ source_file = g_file_get_child (tmpdir, "source");
+ target_file = g_file_get_child (tmpdir, "target");
+ g_file_make_symbolic_link (source_file, "target", NULL, &local_error);
+ g_assert_no_error (local_error);
+
+ /* Ensure that `target` doesn’t exist */
+ g_assert_false (g_file_query_exists (target_file, NULL));
+
+ /* Replace the `source` symlink with a regular file using
+ * %G_FILE_CREATE_REPLACE_DESTINATION, which should replace it *without*
+ * following the symlink */
+ stream = g_file_replace (source_file, NULL, FALSE /* no backup */,
+ G_FILE_CREATE_REPLACE_DESTINATION, NULL, &local_error);
+ g_assert_no_error (local_error);
+
+ g_output_stream_write_all (G_OUTPUT_STREAM (stream), new_contents, strlen (new_contents),
+ &n_written, NULL, &local_error);
+ g_assert_no_error (local_error);
+ g_assert_cmpint (n_written, ==, strlen (new_contents));
+
+ g_output_stream_close (G_OUTPUT_STREAM (stream), NULL, &local_error);
+ g_assert_no_error (local_error);
+
+ g_clear_object (&stream);
+
+ /* At this point, there should still only be one file: `source`. It should
+ * now be a regular file. `target` should not exist. */
+ enumerator = g_file_enumerate_children (tmpdir,
+ G_FILE_ATTRIBUTE_STANDARD_NAME ","
+ G_FILE_ATTRIBUTE_STANDARD_TYPE,
+ G_FILE_QUERY_INFO_NOFOLLOW_SYMLINKS, NULL, &local_error);
+ g_assert_no_error (local_error);
+
+ info = g_file_enumerator_next_file (enumerator, NULL, &local_error);
+ g_assert_no_error (local_error);
+ g_assert_nonnull (info);
+
+ g_assert_cmpstr (g_file_info_get_name (info), ==, "source");
+ g_assert_cmpint (g_file_info_get_file_type (info), ==, G_FILE_TYPE_REGULAR);
+
+ g_clear_object (&info);
+
+ info = g_file_enumerator_next_file (enumerator, NULL, &local_error);
+ g_assert_no_error (local_error);
+ g_assert_null (info);
+
+ g_file_enumerator_close (enumerator, NULL, &local_error);
+ g_assert_no_error (local_error);
+ g_clear_object (&enumerator);
+
+ /* Double-check that `target` doesn’t exist */
+ g_assert_false (g_file_query_exists (target_file, NULL));
+
+ /* Check the content of `source`. */
+ g_file_load_contents (source_file,
+ NULL,
+ &contents,
+ &length,
+ NULL,
+ &local_error);
+ g_assert_no_error (local_error);
+ g_assert_cmpstr (contents, ==, new_contents);
+ g_assert_cmpuint (length, ==, strlen (new_contents));
+ g_free (contents);
+
+ /* Tidy up. */
+ g_file_delete (source_file, NULL, &local_error);
+ g_assert_no_error (local_error);
+
+ g_file_delete (tmpdir, NULL, &local_error);
+ g_assert_no_error (local_error);
+
+ g_clear_object (&target_file);
+ g_clear_object (&source_file);
+ g_clear_object (&tmpdir);
+#else /* if !G_OS_UNIX */
+ g_test_skip ("Symlink replacement tests can only be run on Unix")
+#endif
+}
+
static void
on_file_deleted (GObject *object,
GAsyncResult *result,
@@ -1170,6 +1272,7 @@ main (int argc, char *argv[])
g_test_add_data_func ("/file/async-create-delete/4096", GINT_TO_POINTER (4096), test_create_delete);
g_test_add_func ("/file/replace-load", test_replace_load);
g_test_add_func ("/file/replace-cancel", test_replace_cancel);
+ g_test_add_func ("/file/replace-symlink", test_replace_symlink);
g_test_add_func ("/file/async-delete", test_async_delete);
#ifdef G_OS_UNIX
g_test_add_func ("/file/copy-preserve-mode", test_copy_preserve_mode);
--
2.31.1
From 7f0b0d7fd744ad2f51236444005db49c80a0293d Mon Sep 17 00:00:00 2001
From: Philip Withnall <pwithnall@endlessos.org>
Date: Wed, 24 Feb 2021 17:42:24 +0000
Subject: [PATCH 3/3] glocalfileoutputstream: Add a missing O_CLOEXEC flag to
replace()
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
---
gio/glocalfileoutputstream.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/gio/glocalfileoutputstream.c b/gio/glocalfileoutputstream.c
index 4a7766f68..275770fa4 100644
--- a/gio/glocalfileoutputstream.c
+++ b/gio/glocalfileoutputstream.c
@@ -56,6 +56,12 @@
#define O_BINARY 0
#endif
+#ifndef O_CLOEXEC
+#define O_CLOEXEC 0
+#else
+#define HAVE_O_CLOEXEC 1
+#endif
+
struct _GLocalFileOutputStreamPrivate {
char *tmp_filename;
char *original_filename;
@@ -1127,7 +1133,7 @@ _g_local_file_output_stream_replace (const char *filename,
sync_on_close = FALSE;
/* If the file doesn't exist, create it */
- open_flags = O_CREAT | O_EXCL | O_BINARY;
+ open_flags = O_CREAT | O_EXCL | O_BINARY | O_CLOEXEC;
if (readable)
open_flags |= O_RDWR;
else
@@ -1157,8 +1163,11 @@ _g_local_file_output_stream_replace (const char *filename,
set_error_from_open_errno (filename, error);
return NULL;
}
-
-
+#if !defined(HAVE_O_CLOEXEC) && defined(F_SETFD)
+ else
+ fcntl (fd, F_SETFD, FD_CLOEXEC);
+#endif
+
stream = g_object_new (G_TYPE_LOCAL_FILE_OUTPUT_STREAM, NULL);
stream->priv->fd = fd;
stream->priv->sync_on_close = sync_on_close;
--
2.31.1