Fix i_mutex vs. readdir handling in nfsd

Commit 14f7dd6 ("Copy XFS readdir hack into nfsd code") introduced a
bug to generic code which had been extant for a long time in the XFS
version -- it started to call through into lookup_one_len() and hence
into the file systems' ->lookup() methods without i_mutex held on the
directory.

This patch fixes it by locking the directory's i_mutex again before
calling the filldir functions. The original deadlocks which commit
14f7dd6 was designed to avoid are still avoided, because they were due
to fs-internal locking, not i_mutex.

While we're at it, fix the return type of nfsd_buffered_readdir() which
should be a __be32 not an int -- it's an NFS errno, not a Linux errno.
And return nfserrno(-ENOMEM) when allocation fails, not just -ENOMEM.
Sparse would have caught that, if it wasn't so busy bitching about
__cold__.

Commit 05f4f67 ("nfsd4: don't do lookup within readdir in recovery
code") introduced a similar problem with calling lookup_one_len()
without i_mutex, which this patch also addresses. To fix that, it was
necessary to fix the called functions so that they expect i_mutex to be
held; that part was done by J. Bruce Fields.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Umm-I-can-live-with-that-by: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: J. R. Okajima <hooanon05@yahoo.co.jp>
Tested-by: J. Bruce Fields <bfields@citi.umich.edu>
LKML-Reference: <8036.1237474444@jrobl>
Cc: stable@kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1248,6 +1248,8 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
 	int err;
 	struct qstr this;
 
+	WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));
+
 	err = __lookup_one_len(name, &this, base, len);
 	if (err)
 		return ERR_PTR(err);

fs/nfsd/nfs4recover.c

@@ -229,21 +229,23 @@ nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
 		goto out;
 	status = vfs_readdir(filp, nfsd4_build_namelist, &names);
 	fput(filp);
+	mutex_lock(&dir->d_inode->i_mutex);
 	while (!list_empty(&names)) {
 		entry = list_entry(names.next, struct name_list, list);
 
 		dentry = lookup_one_len(entry->name, dir, HEXDIR_LEN-1);
 		if (IS_ERR(dentry)) {
 			status = PTR_ERR(dentry);
-			goto out;
+			break;
 		}
 		status = f(dir, dentry);
 		dput(dentry);
 		if (status)
-			goto out;
+			break;
 		list_del(&entry->list);
 		kfree(entry);
 	}
+	mutex_unlock(&dir->d_inode->i_mutex);
 out:
 	while (!list_empty(&names)) {
 		entry = list_entry(names.next, struct name_list, list);
@@ -254,36 +256,6 @@ nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
 	return status;
 }
 
-static int
-nfsd4_remove_clid_file(struct dentry *dir, struct dentry *dentry)
-{
-	int status;
-
-	if (!S_ISREG(dir->d_inode->i_mode)) {
-		printk("nfsd4: non-file found in client recovery directory\n");
-		return -EINVAL;
-	}
-	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
-	status = vfs_unlink(dir->d_inode, dentry);
-	mutex_unlock(&dir->d_inode->i_mutex);
-	return status;
-}
-
-static int
-nfsd4_clear_clid_dir(struct dentry *dir, struct dentry *dentry)
-{
-	int status;
-
-	/* For now this directory should already be empty, but we empty it of
-	 * any regular files anyway, just in case the directory was created by
-	 * a kernel from the future.... */
-	nfsd4_list_rec_dir(dentry, nfsd4_remove_clid_file);
-	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
-	status = vfs_rmdir(dir->d_inode, dentry);
-	mutex_unlock(&dir->d_inode->i_mutex);
-	return status;
-}
-
 static int
 nfsd4_unlink_clid_dir(char *name, int namlen)
 {
@@ -294,18 +266,18 @@ nfsd4_unlink_clid_dir(char *name, int namlen)
 
 	mutex_lock(&rec_dir.dentry->d_inode->i_mutex);
 	dentry = lookup_one_len(name, rec_dir.dentry, namlen);
-	mutex_unlock(&rec_dir.dentry->d_inode->i_mutex);
 	if (IS_ERR(dentry)) {
 		status = PTR_ERR(dentry);
-		return status;
+		goto out_unlock;
 	}
 	status = -ENOENT;
 	if (!dentry->d_inode)
 		goto out;
-
-	status = nfsd4_clear_clid_dir(rec_dir.dentry, dentry);
+	status = vfs_rmdir(rec_dir.dentry->d_inode, dentry);
 out:
 	dput(dentry);
+out_unlock:
+	mutex_unlock(&rec_dir.dentry->d_inode->i_mutex);
 	return status;
 }
 
@@ -348,7 +320,7 @@ purge_old(struct dentry *parent, struct dentry *child)
 	if (nfs4_has_reclaimed_state(child->d_name.name, false))
 		return 0;
 
-	status = nfsd4_clear_clid_dir(parent, child);
+	status = vfs_rmdir(parent->d_inode, child);
 	if (status)
 		printk("failed to remove client recovery directory %s\n",
 				child->d_name.name);

fs/nfsd/vfs.c

@@ -1890,8 +1890,8 @@ static int nfsd_buffered_filldir(void *__buf, const char *name, int namlen,
 	return 0;
 }
 
-static int nfsd_buffered_readdir(struct file *file, filldir_t func,
-				 struct readdir_cd *cdp, loff_t *offsetp)
+static __be32 nfsd_buffered_readdir(struct file *file, filldir_t func,
+				    struct readdir_cd *cdp, loff_t *offsetp)
 {
 	struct readdir_data buf;
 	struct buffered_dirent *de;
@@ -1901,11 +1901,12 @@ static int nfsd_buffered_readdir(struct file *file, filldir_t func,
 
 	buf.dirent = (void *)__get_free_page(GFP_KERNEL);
 	if (!buf.dirent)
-		return -ENOMEM;
+		return nfserrno(-ENOMEM);
 
 	offset = *offsetp;
 
 	while (1) {
+		struct inode *dir_inode = file->f_path.dentry->d_inode;
 		unsigned int reclen;
 
 		cdp->err = nfserr_eof; /* will be cleared on successful read */
@@ -1924,26 +1925,38 @@ static int nfsd_buffered_readdir(struct file *file, filldir_t func,
 		if (!size)
 			break;
 
+		/*
+		 * Various filldir functions may end up calling back into
+		 * lookup_one_len() and the file system's ->lookup() method.
+		 * These expect i_mutex to be held, as it would within readdir.
+		 */
+		host_err = mutex_lock_killable(&dir_inode->i_mutex);
+		if (host_err)
+			break;
+
 		de = (struct buffered_dirent *)buf.dirent;
 		while (size > 0) {
 			offset = de->offset;
 
 			if (func(cdp, de->name, de->namlen, de->offset,
 				 de->ino, de->d_type))
-				goto done;
+				break;
 
 			if (cdp->err != nfs_ok)
-				goto done;
+				break;
 
 			reclen = ALIGN(sizeof(*de) + de->namlen,
 				       sizeof(u64));
 			size -= reclen;
 			de = (struct buffered_dirent *)((char *)de + reclen);
 		}
+		mutex_unlock(&dir_inode->i_mutex);
+		if (size > 0) /* We bailed out early */
+			break;
+
 		offset = vfs_llseek(file, 0, SEEK_CUR);
 	}
 
- done:
 	free_page((unsigned long)(buf.dirent));
 
 	if (host_err)