From f25afeb6ab515cf890eff58c0b53cf35b2be0e05 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Sat, 4 Apr 2015 14:42:39 +0200
Subject: rm-rf: never cross mount points

---
 src/shared/path-util.c | 55 ++++++++++++++++++++++++++------------------------
 1 file changed, 29 insertions(+), 26 deletions(-)

(limited to 'src/shared/path-util.c')

diff --git a/src/shared/path-util.c b/src/shared/path-util.c
index 53c0079760..6a984fc1d8 100644
--- a/src/shared/path-util.c
+++ b/src/shared/path-util.c
@@ -470,30 +470,17 @@ char* path_join(const char *root, const char *path, const char *rest) {
                                NULL);
 }
 
-int path_is_mount_point(const char *t, bool allow_symlink) {
-
+int fd_is_mount_point(int fd) {
         union file_handle_union h = FILE_HANDLE_INIT;
         int mount_id = -1, mount_id_parent = -1;
+        bool nosupp = false;
         struct stat a, b;
         int r;
-        _cleanup_close_ int fd = -1;
-        bool nosupp = false;
 
         /* We are not actually interested in the file handles, but
          * name_to_handle_at() also passes us the mount ID, hence use
          * it but throw the handle away */
 
-        if (path_equal(t, "/"))
-                return 1;
-
-        fd = openat(AT_FDCWD, t, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|(allow_symlink ? 0 : O_PATH));
-        if (fd < 0) {
-                if (errno == ENOENT)
-                        return 0;
-
-                return -errno;
-        }
-
         r = name_to_handle_at(fd, "", &h.handle, &mount_id, AT_EMPTY_PATH);
         if (r < 0) {
                 if (errno == ENOSYS)
@@ -502,7 +489,9 @@ int path_is_mount_point(const char *t, bool allow_symlink) {
                         goto fallback;
                 else if (errno == EOPNOTSUPP)
                         /* This kernel or file system does not support
-                         * name_to_handle_at(), hence fallback to the
+                         * name_to_handle_at(), hence let's see if the
+                         * upper fs supports it (in which case it is a
+                         * mount point), otherwise fallback to the
                          * traditional stat() logic */
                         nosupp = true;
                 else if (errno == ENOENT)
@@ -511,29 +500,26 @@ int path_is_mount_point(const char *t, bool allow_symlink) {
                         return -errno;
         }
 
-
         h.handle.handle_bytes = MAX_HANDLE_SZ;
         r = name_to_handle_at(fd, "..", &h.handle, &mount_id_parent, 0);
-        if (r < 0)
-                if (errno == EOPNOTSUPP)
+        if (r < 0) {
+                if (errno == EOPNOTSUPP) {
                         if (nosupp)
                                 /* Neither parent nor child do name_to_handle_at()?
                                    We have no choice but to fall back. */
                                 goto fallback;
                         else
-                                /* The parent can't do name_to_handle_at() but
-                                 * the directory we are interested in can?
-                                 * Or the other way around?
+                                /* The parent can't do name_to_handle_at() but the
+                                 * directory we are interested in can?
                                  * If so, it must be a mount point. */
                                 return 1;
-                else
+                } else
                         return -errno;
-        else
+        } else
                 return mount_id != mount_id_parent;
 
 fallback:
         r = fstatat(fd, "", &a, AT_EMPTY_PATH);
-
         if (r < 0) {
                 if (errno == ENOENT)
                         return 0;
@@ -541,7 +527,6 @@ fallback:
                 return -errno;
         }
 
-
         r = fstatat(fd, "..", &b, 0);
         if (r < 0)
                 return -errno;
@@ -549,6 +534,24 @@ fallback:
         return a.st_dev != b.st_dev;
 }
 
+int path_is_mount_point(const char *t, bool allow_symlink) {
+        _cleanup_close_ int fd = -1;
+        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));
+        if (fd < 0) {
+                if (errno == ENOENT)
+                        return 0;
+
+                return -errno;
+        }
+
+        return fd_is_mount_point(fd);
+}
+
 int path_is_read_only_fs(const char *path) {
         struct statvfs st;
 
-- 
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