new helper: do_new_mount_fc()

Create an fs_context-aware version of do_new_mount().  This takes an
fs_context with a superblock already attached to it.

Make do_new_mount() use do_new_mount_fc() rather than do_new_mount(); this
allows the consolidation of the mount creation, check and add steps.

To make this work, mount_too_revealing() is changed to take a superblock
rather than a mount (which the fs_context doesn't have available), allowing
this check to be done before the mount object is created.

Signed-off-by: David Howells <dhowells@redhat.com>
Co-developed-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 39 insertions, 26 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 0354cb6ac2d3..f629e1c7f3cc 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2523,7 +2523,37 @@ unlock:
         return err;
 }
 
-static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
+static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
+
+/*
+ * Create a new mount using a superblock configuration and request it
+ * be added to the namespace tree.
+ */
+static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
+                           unsigned int mnt_flags)
+{
+        struct vfsmount *mnt;
+        struct super_block *sb = fc->root->d_sb;
+        int error;
+
+        if (mount_too_revealing(sb, &mnt_flags)) {
+                dput(fc->root);
+                fc->root = NULL;
+                deactivate_locked_super(sb);
+                return -EPERM;
+        }
+
+        up_write(&sb->s_umount);
+
+        mnt = vfs_create_mount(fc);
+        if (IS_ERR(mnt))
+                return PTR_ERR(mnt);
+
+        error = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
+        if (error < 0)
+                mntput(mnt);
+        return error;
+}
 
 /*
  * create a new mount for userspace and request it to be added into the
@@ -2533,7 +2563,6 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
                         int mnt_flags, const char *name, void *data)
 {
         struct file_system_type *type;
-        struct vfsmount *mnt;
         struct fs_context *fc;
         const char *subtype = NULL;
         int err = 0;
@@ -2577,26 +2606,9 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
                 err = parse_monolithic_mount_data(fc, data);
         if (!err)
                 err = vfs_get_tree(fc);
-        if (err)
-                goto out;
-
-        up_write(&fc->root->d_sb->s_umount);
-        mnt = vfs_create_mount(fc);
-        if (IS_ERR(mnt)) {
-                err = PTR_ERR(mnt);
-                goto out;
-        }
-
-        if (mount_too_revealing(mnt, &mnt_flags)) {
-                mntput(mnt);
-                err = -EPERM;
-                goto out;
-        }
+        if (!err)
+                err = do_new_mount_fc(fc, path, mnt_flags);
 
-        err = do_add_mount(real_mount(mnt), path, mnt_flags);
-        if (err)
-                mntput(mnt);
-out:
         put_fs_context(fc);
         return err;
 }
@@ -3421,7 +3433,8 @@ bool current_chrooted(void)
         return chrooted;
 }
 
-static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
+static bool mnt_already_visible(struct mnt_namespace *ns,
+                                const struct super_block *sb,
                                 int *new_mnt_flags)
 {
         int new_flags = *new_mnt_flags;
@@ -3433,7 +3446,7 @@ static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
                 struct mount *child;
                 int mnt_flags;
 
-                if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
+                if (mnt->mnt.mnt_sb->s_type != sb->s_type)
                         continue;
 
                 /* This mount is not fully visible if it's root directory
@@ -3484,7 +3497,7 @@ found:
         return visible;
 }
 
-static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
+static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
 {
         const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
@@ -3494,7 +3507,7 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
                 return false;
 
         /* Can this filesystem be too revealing? */
-        s_iflags = mnt->mnt_sb->s_iflags;
+        s_iflags = sb->s_iflags;
         if (!(s_iflags & SB_I_USERNS_VISIBLE))
                 return false;
 
@@ -3504,7 +3517,7 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
                 return true;
         }
 
-        return !mnt_already_visible(ns, mnt, new_mnt_flags);
+        return !mnt_already_visible(ns, sb, new_mnt_flags);
 }
 
 bool mnt_may_suid(struct vfsmount *mnt)