fs: legacy: gracefully handle non existent files

The Semihosting file system API doesn't support listing files, so the
opendir callback returns NULL. This triggers crashes inside the legacy
dentry adapter code, so add some NULL checks to guard against this.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20240611065718.2899625-4-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Author: a3f

fs/legacy.c

@@ -29,6 +29,9 @@ static int legacy_iterate(struct file *file, struct dir_context *ctx)
 	pathname = dpath(dentry, fsdev->vfsmount.mnt_root);
 
 	d = fsdev->driver->opendir(&fsdev->dev, pathname);
+	if (!d)
+		goto out;
+
 	while (1) {
 		dirent = fsdev->driver->readdir(&fsdev->dev, d);
 		if (!dirent)
@@ -38,7 +41,7 @@ static int legacy_iterate(struct file *file, struct dir_context *ctx)
 	}
 
 	fsdev->driver->closedir(&fsdev->dev, d);
-
+out:
 	free(pathname);
 
 	return 0;
@@ -55,10 +58,14 @@ static struct dentry *legacy_lookup(struct inode *dir, struct dentry *dentry,
 	int ret;
 
 	pathname = dpath(dentry, fsdev->vfsmount.mnt_root);
+	if (!pathname)
+		return NULL;
 
 	ret = fsdev->driver->stat(&fsdev->dev, pathname, &s);
 	if (!ret) {
 		inode = legacy_get_inode(sb, dir, s.st_mode);
+		if (!inode)
+			return NULL;
 
 		inode->i_size = s.st_size;
 		inode->i_mode = s.st_mode;