VFS: add common error checks to lookup_one_qstr_excl()

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>
Link: https://lore.kernel.org/r/20250217003020.3170652-3-neilb@suse.de
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 10 insertions, 16 deletions

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 @@ retry:
 	}
 
 	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 @@ retry:
 		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;