VFS: tidy up do_unlinkat()

The simplification of locking in the previous patch opens up some room
for tidying up do_unlinkat()

- change all "exit" labels to describe what will happen at the label.
- always goto an exit label on an error - unwrap the "if (!IS_ERR())" branch.
- Move the "slashes" handing inline, but mark it as unlikely()
- simplify use of the "inode" variable - we no longer need to test for NULL.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20251113002050.676694-4-neilb@ownmail.net
Tested-by: syzbot@syzkaller.appspotmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: neilbrown

fs/namei.c

@@ -4755,65 +4755,62 @@ int do_unlinkat(int dfd, struct filename *name)
 	struct path path;
 	struct qstr last;
 	int type;
-	struct inode *inode = NULL;
+	struct inode *inode;
 	struct inode *delegated_inode = NULL;
 	unsigned int lookup_flags = 0;
 retry:
 	error = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
 	if (error)
-		goto exit1;
+		goto exit_putname;
 
 	error = -EISDIR;
 	if (type != LAST_NORM)
-		goto exit2;
+		goto exit_path_put;
 
 	error = mnt_want_write(path.mnt);
 	if (error)
-		goto exit2;
+		goto exit_path_put;
 retry_deleg:
 	dentry = start_dirop(path.dentry, &last, lookup_flags);
 	error = PTR_ERR(dentry);
-	if (!IS_ERR(dentry)) {
+	if (IS_ERR(dentry))
+		goto exit_drop_write;
 
-		/* Why not before? Because we want correct error value */
-		if (last.name[last.len])
-			goto slashes;
-		inode = dentry->d_inode;
-		ihold(inode);
-		error = security_path_unlink(&path, dentry);
-		if (error)
-			goto exit3;
-		error = vfs_unlink(mnt_idmap(path.mnt), path.dentry->d_inode,
-				   dentry, &delegated_inode);
-exit3:
+	/* Why not before? Because we want correct error value */
+	if (unlikely(last.name[last.len])) {
+		if (d_is_dir(dentry))
+			error = -EISDIR;
+		else
+			error = -ENOTDIR;
 		end_dirop(dentry);
+		goto exit_drop_write;
 	}
-	if (inode)
-		iput(inode);	/* truncate the inode here */
-	inode = NULL;
+	inode = dentry->d_inode;
+	ihold(inode);
+	error = security_path_unlink(&path, dentry);
+	if (error)
+		goto exit_end_dirop;
+	error = vfs_unlink(mnt_idmap(path.mnt), path.dentry->d_inode,
+			   dentry, &delegated_inode);
+exit_end_dirop:
+	end_dirop(dentry);
+	iput(inode);	/* truncate the inode here */
 	if (delegated_inode) {
 		error = break_deleg_wait(&delegated_inode);
 		if (!error)
 			goto retry_deleg;
 	}
+exit_drop_write:
 	mnt_drop_write(path.mnt);
-exit2:
+exit_path_put:
 	path_put(&path);
 	if (retry_estale(error, lookup_flags)) {
 		lookup_flags |= LOOKUP_REVAL;
-		inode = NULL;
 		goto retry;
 	}
-exit1:
+exit_putname:
 	putname(name);
 	return error;
-
-slashes:
-	if (d_is_dir(dentry))
-		error = -EISDIR;
-	else
-		error = -ENOTDIR;
-	goto exit3;
 }
 
 SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)