allow the temp files created by open() to be linked to

O_TMPFILE | O_CREAT => linkat() with AT_SYMLINK_FOLLOW and /proc/self/fd/<n>
as oldpath (i.e. flink()) will create a link
O_TMPFILE | O_CREAT | O_EXCL => ENOENT on attempt to link those guys

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 18 insertions, 3 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 00d5fc3b86e1..d6dfb09c8280 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -333,8 +333,10 @@ EXPORT_SYMBOL(set_nlink);
  */
 void inc_nlink(struct inode *inode)
 {
-        if (WARN_ON(inode->i_nlink == 0))
+        if (unlikely(inode->i_nlink == 0)) {
+                WARN_ON(!(inode->i_state & I_LINKABLE));
                 atomic_long_dec(&inode->i_sb->s_remove_count);
+        }
 
         inode->__i_nlink++;
 }
diff --git a/fs/namei.c b/fs/namei.c
index 778e253e3d48..66998b06d822 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2948,8 +2948,14 @@ static int do_tmpfile(int dfd, struct filename *pathname,
         if (error)
                 goto out2;
         error = open_check_o_direct(file);
-        if (error)
+        if (error) {
                 fput(file);
+        } else if (!(op->open_flag & O_EXCL)) {
+                struct inode *inode = file_inode(file);
+                spin_lock(&inode->i_lock);
+                inode->i_state |= I_LINKABLE;
+                spin_unlock(&inode->i_lock);
+        }
 out2:
         mnt_drop_write(nd->path.mnt);
 out:
@@ -3628,12 +3634,18 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
 
         mutex_lock(&inode->i_mutex);
         /* Make sure we don't allow creating hardlink to an unlinked file */
-        if (inode->i_nlink == 0)
+        if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE))
                 error =  -ENOENT;
         else if (max_links && inode->i_nlink >= max_links)
                 error = -EMLINK;
         else
                 error = dir->i_op->link(old_dentry, dir, new_dentry);
+
+        if (!error && (inode->i_state & I_LINKABLE)) {
+                spin_lock(&inode->i_lock);
+                inode->i_state &= ~I_LINKABLE;
+                spin_unlock(&inode->i_lock);
+        }
         mutex_unlock(&inode->i_mutex);
         if (!error)
                 fsnotify_link(dir, inode, new_dentry);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index dd6615f0fd13..ab11c44b0697 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1744,6 +1744,7 @@ struct super_operations {
 #define I_REFERENCED            (1 << 8)
 #define __I_DIO_WAKEUP          9
 #define I_DIO_WAKEUP            (1 << I_DIO_WAKEUP)
+#define I_LINKABLE              (1 << 10)
 
 #define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)