VFS: add vfs_lookup_open() for nfsd

vfs_lookup_open() is a limited version of lookup_open() which is
exported for nfsd to use - to replace dentry_create().

It is limited in that no filename is given (thus no auditing) and no
LOOKUP_ flags are passed.  A few "intent" LOOKUP flags are deduced from
the open flags.

If a non-regular file is found and appropriate error is returned and no
file is opened.

Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20260714230534.776886-4-neilb@ownmail.net
Reviewed-by: Jori Koolstra <jkoolstra@xs4all.nl>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/fs/namei.c b/fs/namei.c
index 1ca738401afa93a126d3866fa78ab32b5ab64c99..3ca34388eda3ee94fc1d6c895118f07b647c3181 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4568,6 +4568,102 @@ out_dput:
        goto out;
 }
 
+/**
+ * vfs_lookup_open - open and possibly create a regular file
+ * @parent: directory to contain file
+ * @last: final component of file name
+ * @open_flag: O_flags
+ * @mode: initial permissions for file
+ *
+ * Open a file after lookup and/or create.  This provides similar
+ * functionality open_last_lookups() for non-VFS users, particularly
+ * nfsd.
+ * It uses ->atomic_open or ->lookup / ->create / ->open as appropriate.
+ *
+ * If the fs object found is not a regular file then an error is returned.
+ * In some cases, related errors are repurposed so that the caller can
+ * determine the type of file found from the error.
+ * -EISDIR : a directory was found
+ * -ELOOP  : a symlink was found
+ * -ENODEV : a block or character device special file was found
+ * -EFTYPE : any other non-regular file was found, such as FIFO or SOCK.
+ *           or ->atomic_open responded to __O_REGULAR.
+ *
+ * Returns: the opened struct file, or an error.
+ */
+struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
+                            int open_flag, umode_t mode)
+{
+       struct file *file __free(fput) = NULL;
+       struct nameidata nd = {};
+       struct open_flags op = {};
+       struct dentry *dentry;
+       int error = 0;
+
+       WARN_ONCE(mode & ~S_IALLUGO, "mode must only have permission bits");
+       WARN_ONCE(open_flag & ~(O_ACCMODE|O_CREAT|O_EXCL|O_TRUNC|__O_REGULAR),
+                 "open_flag has unsupported flags");
+
+       mode |= S_IFREG;
+       open_flag |= __O_REGULAR;
+
+       error = lookup_noperm_common(last, parent->dentry);
+       if (error)
+               return ERR_PTR(error);
+
+       file = alloc_empty_file(open_flag, current_cred());
+       if (IS_ERR(file))
+               return file;
+
+       nd.path = *parent;
+       nd.last = *last;
+       nd.flags = LOOKUP_OPEN;
+       if (open_flag & O_CREAT) {
+               nd.flags |= LOOKUP_CREATE;
+               if (open_flag & O_EXCL)
+                       nd.flags |= LOOKUP_EXCL;
+       }
+       op.open_flag = open_flag;
+       op.mode = mode;
+       dentry = lookup_open(&nd, file, &op);
+
+       if (IS_ERR(dentry))
+               return ERR_CAST(dentry);
+
+       if (d_really_is_negative(dentry)) {
+               error = -ENOENT;
+       } else if (!(file->f_mode & FMODE_CREATED) && (open_flag & O_EXCL)) {
+               error = -EEXIST;
+       } else if ((dentry->d_inode->i_mode & S_IFMT) != S_IFREG) {
+               switch (dentry->d_inode->i_mode & S_IFMT) {
+               case S_IFDIR:
+                       error = -EISDIR;
+                       break;
+               case S_IFLNK:
+                       error = -ELOOP;
+                       break;
+               case S_IFBLK:
+               case S_IFCHR:
+                       error = -ENODEV;
+                       break;
+               case S_IFIFO:
+               case S_IFSOCK:
+               default:
+                       error = -EFTYPE;
+                       break;
+               }
+       } else if (!(file->f_mode & FMODE_OPENED)) {
+               nd.path.dentry = dentry;
+               error = vfs_open(&nd.path, file);
+       }
+       dput(dentry);
+
+       if (error)
+               return ERR_PTR(error);
+       return no_free_ptr(file);
+}
+EXPORT_SYMBOL_FOR_MODULES(vfs_lookup_open, "nfsd");
+
 static inline bool trailing_slashes(struct nameidata *nd)
 {
        return (bool)nd->last.name[nd->last.len];

diff --git a/include/linux/namei.h b/include/linux/namei.h
index ebe6e29f7e93ba1613c6cde63aaff4d2a909975e..86d657b24fc6a163f6206c821fe4453e327de5e4 100644 (file)
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -97,6 +97,9 @@ struct dentry *start_creating_dentry(struct dentry *parent,
 struct dentry *start_removing_dentry(struct dentry *parent,
                                     struct dentry *child);
 
+struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
+                            int open_flag, umode_t mode);
+
 /* end_creating - finish action started with start_creating
  * @child: dentry returned by start_creating() or vfs_mkdir()
  *