[PATCH 2/2] VFS: add common error checks to lookup_one_qstr_excl()

[NeilBrown <neilb@suse.de>]

Callers of lookup_one_qstr_excl() often check if the result is negative or
positive.
These changes can easily be moved into lookup_one_qstr_excl() by checking the
lookup flags:
LOOKUP_CREATE means it is NOT an error if the name doesn't exist.
LOOKUP_EXCL means it IS an error if the name DOES exist.

This patch adds these checks, then removes error checks from callers,
and ensures that appropriate flags are passed.

This subtly changes the meaning of LOOKUP_EXCL.  Previously it could
only accompany LOOKUP_CREATE.  Now it can accompany LOOKUP_RENAME_TARGET
as well.  A couple of small changes are needed to accommodate this.  The
NFS change is functionally a no-op but ensures nfs_is_exclusive_create() does
exactly what the name says.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/namei.c          | 59 +++++++++++++++------------------------------
 fs/nfs/dir.c        |  3 ++-
 fs/smb/server/vfs.c | 26 ++++++++------------
 3 files changed, 31 insertions(+), 57 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index e3047db7b2b4..e0527f4b0586 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1665,6 +1665,8 @@ static struct dentry *lookup_dcache(const struct qstr *name,
  * dentries - as the matter of fact, this only gets called
  * when directory is guaranteed to have no in-lookup children
  * at all.
+ * Will return -ENOENT if name isn't found and LOOKUP_CREATE wasn't passed.
+ * Will return -EEXIST if name is found and LOOKUP_EXCL was passed.
  */
 struct dentry *lookup_one_qstr_excl(const struct qstr *name,
 				    struct dentry *base,
@@ -1675,7 +1677,7 @@ struct dentry *lookup_one_qstr_excl(const struct qstr *name,
 	struct inode *dir = base->d_inode;
 
 	if (dentry)
-		return dentry;
+		goto found;
 
 	/* Don't create child dentry for a dead directory. */
 	if (unlikely(IS_DEADDIR(dir)))
@@ -1690,6 +1692,15 @@ struct dentry *lookup_one_qstr_excl(const struct qstr *name,
 		dput(dentry);
 		dentry = old;
 	}
+found:
+	if (d_is_negative(dentry) && !(flags & LOOKUP_CREATE)) {
+		dput(dentry);
+		return ERR_PTR(-ENOENT);
+	}
+	if (d_is_positive(dentry) && (flags & LOOKUP_EXCL)) {
+		dput(dentry);
+		return ERR_PTR(-EEXIST);
+	}
 	return dentry;
 }
 EXPORT_SYMBOL(lookup_one_qstr_excl);
@@ -2736,10 +2747,6 @@ static struct dentry *__kern_path_locked(int dfd, struct filename *name, struct
 	}
 	inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
 	d = lookup_one_qstr_excl(&last, path->dentry, 0);
-	if (!IS_ERR(d) && d_is_negative(d)) {
-		dput(d);
-		d = ERR_PTR(-ENOENT);
-	}
 	if (IS_ERR(d)) {
 		inode_unlock(path->dentry->d_inode);
 		path_put(path);
@@ -4077,27 +4084,13 @@ static struct dentry *filename_create(int dfd, struct filename *name,
 	 * '/', and a directory wasn't requested.
 	 */
 	if (last.name[last.len] && !want_dir)
-		create_flags = 0;
+		create_flags &= ~LOOKUP_CREATE;
 	inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
 	dentry = lookup_one_qstr_excl(&last, path->dentry,
 				      reval_flag | create_flags);
 	if (IS_ERR(dentry))
 		goto unlock;
 
-	error = -EEXIST;
-	if (d_is_positive(dentry))
-		goto fail;
-
-	/*
-	 * Special case - lookup gave negative, but... we had foo/bar/
-	 * From the vfs_mknod() POV we just have a negative dentry -
-	 * all is fine. Let's be bastards - you had / on the end, you've
-	 * been asking for (non-existent) directory. -ENOENT for you.
-	 */
-	if (unlikely(!create_flags)) {
-		error = -ENOENT;
-		goto fail;
-	}
 	if (unlikely(err2)) {
 		error = err2;
 		goto fail;
@@ -4444,10 +4437,6 @@ int do_rmdir(int dfd, struct filename *name)
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
 		goto exit3;
-	if (!dentry->d_inode) {
-		error = -ENOENT;
-		goto exit4;
-	}
 	error = security_path_rmdir(&path, dentry);
 	if (error)
 		goto exit4;
@@ -4578,7 +4567,7 @@ int do_unlinkat(int dfd, struct filename *name)
 	if (!IS_ERR(dentry)) {
 
 		/* Why not before? Because we want correct error value */
-		if (last.name[last.len] || d_is_negative(dentry))
+		if (last.name[last.len])
 			goto slashes;
 		inode = dentry->d_inode;
 		ihold(inode);
@@ -4612,9 +4601,7 @@ int do_unlinkat(int dfd, struct filename *name)
 	return error;
 
 slashes:
-	if (d_is_negative(dentry))
-		error = -ENOENT;
-	else if (d_is_dir(dentry))
+	if (d_is_dir(dentry))
 		error = -EISDIR;
 	else
 		error = -ENOTDIR;
@@ -5114,7 +5101,8 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 	struct qstr old_last, new_last;
 	int old_type, new_type;
 	struct inode *delegated_inode = NULL;
-	unsigned int lookup_flags = 0, target_flags = LOOKUP_RENAME_TARGET;
+	unsigned int lookup_flags = 0, target_flags =
+		LOOKUP_RENAME_TARGET | LOOKUP_CREATE;
 	bool should_retry = false;
 	int error = -EINVAL;
 
@@ -5127,6 +5115,8 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 
 	if (flags & RENAME_EXCHANGE)
 		target_flags = 0;
+	if (flags & RENAME_NOREPLACE)
+		target_flags |= LOOKUP_EXCL;
 
 retry:
 	error = filename_parentat(olddfd, from, lookup_flags, &old_path,
@@ -5168,23 +5158,12 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 	error = PTR_ERR(old_dentry);
 	if (IS_ERR(old_dentry))
 		goto exit3;
-	/* source must exist */
-	error = -ENOENT;
-	if (d_is_negative(old_dentry))
-		goto exit4;
 	new_dentry = lookup_one_qstr_excl(&new_last, new_path.dentry,
 					  lookup_flags | target_flags);
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
 		goto exit4;
-	error = -EEXIST;
-	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
-		goto exit5;
 	if (flags & RENAME_EXCHANGE) {
-		error = -ENOENT;
-		if (d_is_negative(new_dentry))
-			goto exit5;
-
 		if (!d_is_dir(new_dentry)) {
 			error = -ENOTDIR;
 			if (new_last.name[new_last.len])
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 2b04038b0e40..56cf16a72334 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1532,7 +1532,8 @@ static int nfs_is_exclusive_create(struct inode *dir, unsigned int flags)
 {
 	if (NFS_PROTO(dir)->version == 2)
 		return 0;
-	return flags & LOOKUP_EXCL;
+	return (flags & (LOOKUP_CREATE | LOOKUP_EXCL)) ==
+		(LOOKUP_CREATE | LOOKUP_EXCL);
 }
 
 /*
diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 6890016e1923..fe29acef5872 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -113,11 +113,6 @@ static int ksmbd_vfs_path_lookup_locked(struct ksmbd_share_config *share_conf,
 	if (IS_ERR(d))
 		goto err_out;
 
-	if (d_is_negative(d)) {
-		dput(d);
-		goto err_out;
-	}
-
 	path->dentry = d;
 	path->mnt = mntget(parent_path->mnt);
 
@@ -693,6 +688,7 @@ int ksmbd_vfs_rename(struct ksmbd_work *work, const struct path *old_path,
 	struct ksmbd_file *parent_fp;
 	int new_type;
 	int err, lookup_flags = LOOKUP_NO_SYMLINKS;
+	int target_lookup_flags = LOOKUP_RENAME_TARGET;
 
 	if (ksmbd_override_fsids(work))
 		return -ENOMEM;
@@ -703,6 +699,14 @@ int ksmbd_vfs_rename(struct ksmbd_work *work, const struct path *old_path,
 		goto revert_fsids;
 	}
 
+	/*
+	 * explicitly handle file overwrite case, for compatibility with
+	 * filesystems that may not support rename flags (e.g: fuse)
+	 */
+	if (flags & RENAME_NOREPLACE)
+		target_lookup_flags |= LOOKUP_EXCL;
+	flags &= ~(RENAME_NOREPLACE);
+
 retry:
 	err = vfs_path_parent_lookup(to, lookup_flags | LOOKUP_BENEATH,
 				     &new_path, &new_last, &new_type,
@@ -743,7 +747,7 @@ int ksmbd_vfs_rename(struct ksmbd_work *work, const struct path *old_path,
 	}
 
 	new_dentry = lookup_one_qstr_excl(&new_last, new_path.dentry,
-					  lookup_flags | LOOKUP_RENAME_TARGET);
+					  lookup_flags | target_lookup_flags);
 	if (IS_ERR(new_dentry)) {
 		err = PTR_ERR(new_dentry);
 		goto out3;
@@ -754,16 +758,6 @@ int ksmbd_vfs_rename(struct ksmbd_work *work, const struct path *old_path,
 		goto out4;
 	}
 
-	/*
-	 * explicitly handle file overwrite case, for compatibility with
-	 * filesystems that may not support rename flags (e.g: fuse)
-	 */
-	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry)) {
-		err = -EEXIST;
-		goto out4;
-	}
-	flags &= ~(RENAME_NOREPLACE);
-
 	if (old_child == trap) {
 		err = -EINVAL;
 		goto out4;
-- 
2.47.1