From 117a45829a6be1ef728616c3c90fc8c6f9eda318 Mon Sep 17 00:00:00 2001

From: Martin Pitt <martin.pitt@ubuntu.com>

Date: Wed, 27 May 2015 09:56:03 +0200

Subject: [PATCH] path-util: Fix path_is_mount_point for files

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Commits 27cc6f166 and f25afeb broke path_is_mount_point() for files (such as

/etc/machine-id → /run/machine-id bind mounts) as with the factorization of

fd_is_mount_point() we lost the parent directory. We cannot determine that from

an fd only as openat(fd, "..") only works for directory fds.

Change fd_is_mount_point() to behave like openat(): It now takes a file

descriptor of the containing directory, a file name in it, and flags (which can

be 0 or AT_SYMLINK_FOLLOW). Unlike name_to_handle_at() or openat(), fstatat()

only accepts the inverse flag AT_SYMLINK_NOFOLLOW and complains with EINVAL

about AT_SYMLINK_FOLLOW; so we need to transform the flags for that fallback.

Adjust rm_rf_children() accordingly (only other caller of fd_is_mount_point()

aside from path_is_mount_point()).

Add test cases for files, links, and file bind mounts (the latter will only

work when running as root). Split out a new test_path_is_mount_point() test

case function as it got significantly larger now.

(cherry picked from commit 5d409034017e9f9f8c4392157d95511fc2e05d87)

---

 src/shared/path-util.c    | 31 +++++++++++++------

 src/shared/path-util.h    |  2 +-

 src/shared/rm-rf.c        |  2 +-

 src/test/test-path-util.c | 76 +++++++++++++++++++++++++++++++++++++++--------

 4 files changed, 87 insertions(+), 24 deletions(-)

diff --git a/src/shared/path-util.c b/src/shared/path-util.c

index 7090989fcb..8be479cd7f 100644

--- a/src/shared/path-util.c

+++ b/src/shared/path-util.c

@@ -509,7 +509,7 @@ static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id

         return safe_atoi(p, mnt_id);

 }

-int fd_is_mount_point(int fd) {

+int fd_is_mount_point(int fd, const char *filename, int flags) {

         union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;

         int mount_id = -1, mount_id_parent = -1;

         bool nosupp = false, check_st_dev = true;

@@ -517,6 +517,7 @@ int fd_is_mount_point(int fd) {

         int r;

         assert(fd >= 0);

+        assert(filename);

         /* First we will try the name_to_handle_at() syscall, which

          * tells us the mount id and an opaque file "handle". It is

@@ -541,7 +542,7 @@ int fd_is_mount_point(int fd) {

          * subvolumes have different st_dev, even though they aren't

          * real mounts of their own. */

-        r = name_to_handle_at(fd, "", &h.handle, &mount_id, AT_EMPTY_PATH);

+        r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags);

         if (r < 0) {

                 if (errno == ENOSYS)

                         /* This kernel does not support name_to_handle_at()

@@ -558,7 +559,7 @@ int fd_is_mount_point(int fd) {

                         return -errno;

         }

-        r = name_to_handle_at(fd, "..", &h_parent.handle, &mount_id_parent, 0);

+        r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH);

         if (r < 0) {

                 if (errno == EOPNOTSUPP) {

                         if (nosupp)

@@ -593,13 +594,13 @@ int fd_is_mount_point(int fd) {

         return mount_id != mount_id_parent;

 fallback_fdinfo:

-        r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id);

+        r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id);

         if (r == -EOPNOTSUPP)

                 goto fallback_fstat;

         if (r < 0)

                 return r;

-        r = fd_fdinfo_mnt_id(fd, "..", 0, &mount_id_parent);

+        r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent);

         if (r < 0)

                 return r;

@@ -615,10 +616,16 @@ fallback_fdinfo:

         check_st_dev = false;

 fallback_fstat:

-        if (fstatat(fd, "", &a, AT_EMPTY_PATH) < 0)

+        /* yay for fstatat() taking a different set of flags than the other

+         * _at() above */

+        if (flags & AT_SYMLINK_FOLLOW)

+                flags &= ~AT_SYMLINK_FOLLOW;

+        else

+                flags |= AT_SYMLINK_NOFOLLOW;

+        if (fstatat(fd, filename, &a, flags) < 0)

                 return -errno;

-        if (fstatat(fd, "..", &b, 0) < 0)

+        if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0)

                 return -errno;

         /* A directory with same device and inode as its parent? Must

@@ -632,17 +639,23 @@ fallback_fstat:

 int path_is_mount_point(const char *t, bool allow_symlink) {

         _cleanup_close_ int fd = -1;

+        _cleanup_free_ char *parent = NULL;

+        int r;

         assert(t);

         if (path_equal(t, "/"))

                 return 1;

-        fd = openat(AT_FDCWD, t, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|(allow_symlink ? 0 : O_PATH));

+        r = path_get_parent(t, &parent);

+        if (r < 0)

+                return r;

+

+        fd = openat(AT_FDCWD, parent, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_PATH);

         if (fd < 0)

                 return -errno;

-        return fd_is_mount_point(fd);

+        return fd_is_mount_point(fd, basename(t), (allow_symlink ? AT_SYMLINK_FOLLOW : 0));

 }

 int path_is_read_only_fs(const char *path) {

diff --git a/src/shared/path-util.h b/src/shared/path-util.h

index 4f45cfd2b7..38ad799ba0 100644

--- a/src/shared/path-util.h

+++ b/src/shared/path-util.h

@@ -53,7 +53,7 @@ char** path_strv_make_absolute_cwd(char **l);

 char** path_strv_resolve(char **l, const char *prefix);

 char** path_strv_resolve_uniq(char **l, const char *prefix);

-int fd_is_mount_point(int fd);

+int fd_is_mount_point(int fd, const char *filename, int flags);

 int path_is_mount_point(const char *path, bool allow_symlink);

 int path_is_read_only_fs(const char *path);

 int path_is_os_tree(const char *path);

diff --git a/src/shared/rm-rf.c b/src/shared/rm-rf.c

index a89e8afc2a..bafd483be2 100644

--- a/src/shared/rm-rf.c

+++ b/src/shared/rm-rf.c

@@ -103,7 +103,7 @@ int rm_rf_children(int fd, RemoveFlags flags, struct stat *root_dev) {

                         }

                         /* Stop at mount points */

-                        r = fd_is_mount_point(subdir_fd);

+                        r = fd_is_mount_point(fd, de->d_name, 0);

                         if (r < 0) {

                                 if (ret == 0 && r != -ENOENT)

                                         ret = r;

diff --git a/src/test/test-path-util.c b/src/test/test-path-util.c

index 09f0f2f89e..80782ff902 100644

--- a/src/test/test-path-util.c

+++ b/src/test/test-path-util.c

@@ -21,6 +21,7 @@

 #include <stdio.h>

 #include <unistd.h>

+#include <sys/mount.h>

 #include "path-util.h"

 #include "util.h"

@@ -88,21 +89,9 @@ static void test_path(void) {

         test_parent("/aa///file...", "/aa///");

         test_parent("file.../", NULL);

-        assert_se(path_is_mount_point("/", true) > 0);

-        assert_se(path_is_mount_point("/", false) > 0);

-

         fd = open("/", O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOCTTY);

         assert_se(fd >= 0);

-        assert_se(fd_is_mount_point(fd) > 0);

-

-        assert_se(path_is_mount_point("/proc", true) > 0);

-        assert_se(path_is_mount_point("/proc", false) > 0);

-

-        assert_se(path_is_mount_point("/proc/1", true) == 0);

-        assert_se(path_is_mount_point("/proc/1", false) == 0);

-

-        assert_se(path_is_mount_point("/sys", true) > 0);

-        assert_se(path_is_mount_point("/sys", false) > 0);

+        assert_se(fd_is_mount_point(fd, "/", 0) > 0);

         {

                 char p1[] = "aaa/bbb////ccc";

@@ -322,6 +311,66 @@ static void test_prefix_root(void) {

         test_prefix_root_one("/foo///", "//bar", "/foo/bar");

 }

+static void test_path_is_mount_point(void) {

+        int fd, rt, rf, rlt, rlf;

+        char tmp_dir[] = "/tmp/test-path-is-mount-point-XXXXXX";

+        _cleanup_free_ char *file1 = NULL, *file2 = NULL, *link1 = NULL, *link2 = NULL;

+

+        assert_se(path_is_mount_point("/", true) > 0);

+        assert_se(path_is_mount_point("/", false) > 0);

+

+        assert_se(path_is_mount_point("/proc", true) > 0);

+        assert_se(path_is_mount_point("/proc", false) > 0);

+

+        assert_se(path_is_mount_point("/proc/1", true) == 0);

+        assert_se(path_is_mount_point("/proc/1", false) == 0);

+

+        assert_se(path_is_mount_point("/sys", true) > 0);

+        assert_se(path_is_mount_point("/sys", false) > 0);

+

+        /* file mountpoints */

+        assert_se(mkdtemp(tmp_dir) != NULL);

+        file1 = path_join(NULL, tmp_dir, "file1");

+        assert_se(file1);

+        file2 = path_join(NULL, tmp_dir, "file2");

+        assert_se(file2);

+        fd = open(file1, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0664);

+        assert_se(fd > 0);

+        close(fd);

+        fd = open(file2, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0664);

+        assert_se(fd > 0);

+        close(fd);

+        link1 = path_join(NULL, tmp_dir, "link1");

+        assert_se(link1);

+        assert_se(symlink("file1", link1) == 0);

+        link2 = path_join(NULL, tmp_dir, "link2");

+        assert_se(link1);

+        assert_se(symlink("file2", link2) == 0);

+

+        assert_se(path_is_mount_point(file1, true) == 0);

+        assert_se(path_is_mount_point(file1, false) == 0);

+        assert_se(path_is_mount_point(link1, true) == 0);

+        assert_se(path_is_mount_point(link1, false) == 0);

+

+        /* this test will only work as root */

+        if (mount(file1, file2, NULL, MS_BIND, NULL) >= 0) {

+                rf = path_is_mount_point(file2, false);

+                rt = path_is_mount_point(file2, true);

+                rlf = path_is_mount_point(link2, false);

+                rlt = path_is_mount_point(link2, true);

+

+                assert_se(umount(file2) == 0);

+

+                assert_se(rf == 1);

+                assert_se(rt == 1);

+                assert_se(rlf == 0);

+                assert_se(rlt == 1);

+        } else

+                printf("Skipping bind mount file test: %m\n");

+

+        assert_se(rm_rf(tmp_dir, REMOVE_ROOT|REMOVE_PHYSICAL) == 0);

+}

+

 int main(int argc, char **argv) {

         test_path();

         test_find_binary(argv[0], true);

@@ -333,6 +382,7 @@ int main(int argc, char **argv) {

         test_strv_resolve();

         test_path_startswith();

         test_prefix_root();

+        test_path_is_mount_point();

         return 0;

 }