io_uring: add support for IORING_OP_SYMLINKAT

IORING_OP_SYMLINKAT behaves like symlinkat(2) and takes the same flags
and arguments.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210514145259.wtl4xcsp52woi6ab@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20210708063447.3556403-11-dkadashev@gmail.com
[axboe: add splice_fd_in check]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/internal.h

@@ -77,6 +77,7 @@ int may_linkat(struct user_namespace *mnt_userns, struct path *link);
 int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
 		 struct filename *newname, unsigned int flags);
 int do_mkdirat(int dfd, struct filename *name, umode_t mode);
+int do_symlinkat(struct filename *from, int newdfd, struct filename *to);
 
 /*
  * namespace.c

fs/io_uring.c

@@ -669,6 +669,13 @@ struct io_mkdir {
 	struct filename			*filename;
 };
 
+struct io_symlink {
+	struct file			*file;
+	int				new_dfd;
+	struct filename			*oldpath;
+	struct filename			*newpath;
+};
+
 struct io_completion {
 	struct file			*file;
 	u32				cflags;
@@ -829,6 +836,7 @@ struct io_kiocb {
 		struct io_rename	rename;
 		struct io_unlink	unlink;
 		struct io_mkdir		mkdir;
+		struct io_symlink	symlink;
 		/* use only after cleaning per-op data, see io_clean_op() */
 		struct io_completion	compl;
 	};
@@ -1041,6 +1049,7 @@ static const struct io_op_def io_op_defs[] = {
 	[IORING_OP_RENAMEAT] = {},
 	[IORING_OP_UNLINKAT] = {},
 	[IORING_OP_MKDIRAT] = {},
+	[IORING_OP_SYMLINKAT] = {},
 };
 
 /* requests with any of those set should undergo io_disarm_next() */
@@ -3655,6 +3664,55 @@ static int io_mkdirat(struct io_kiocb *req, int issue_flags)
 	return 0;
 }
 
+static int io_symlinkat_prep(struct io_kiocb *req,
+			    const struct io_uring_sqe *sqe)
+{
+	struct io_symlink *sl = &req->symlink;
+	const char __user *oldpath, *newpath;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->len || sqe->rw_flags || sqe->buf_index ||
+	    sqe->splice_fd_in)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	sl->new_dfd = READ_ONCE(sqe->fd);
+	oldpath = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	newpath = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+
+	sl->oldpath = getname(oldpath);
+	if (IS_ERR(sl->oldpath))
+		return PTR_ERR(sl->oldpath);
+
+	sl->newpath = getname(newpath);
+	if (IS_ERR(sl->newpath)) {
+		putname(sl->oldpath);
+		return PTR_ERR(sl->newpath);
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	return 0;
+}
+
+static int io_symlinkat(struct io_kiocb *req, int issue_flags)
+{
+	struct io_symlink *sl = &req->symlink;
+	int ret;
+
+	if (issue_flags & IO_URING_F_NONBLOCK)
+		return -EAGAIN;
+
+	ret = do_symlinkat(sl->oldpath, sl->new_dfd, sl->newpath);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	if (ret < 0)
+		req_set_fail(req);
+	io_req_complete(req, ret);
+	return 0;
+}
+
 static int io_shutdown_prep(struct io_kiocb *req,
 			    const struct io_uring_sqe *sqe)
 {
@@ -6054,6 +6112,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return io_unlinkat_prep(req, sqe);
 	case IORING_OP_MKDIRAT:
 		return io_mkdirat_prep(req, sqe);
+	case IORING_OP_SYMLINKAT:
+		return io_symlinkat_prep(req, sqe);
 	}
 
 	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
@@ -6220,6 +6280,10 @@ static void io_clean_op(struct io_kiocb *req)
 		case IORING_OP_MKDIRAT:
 			putname(req->mkdir.filename);
 			break;
+		case IORING_OP_SYMLINKAT:
+			putname(req->symlink.oldpath);
+			putname(req->symlink.newpath);
+			break;
 		}
 	}
 	if ((req->flags & REQ_F_POLLED) && req->apoll) {
@@ -6351,6 +6415,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 	case IORING_OP_MKDIRAT:
 		ret = io_mkdirat(req, issue_flags);
 		break;
+	case IORING_OP_SYMLINKAT:
+		ret = io_symlinkat(req, issue_flags);
+		break;
 	default:
 		ret = -EINVAL;
 		break;

fs/namei.c

@@ -4223,8 +4223,7 @@ int vfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_symlink);
 
-static int do_symlinkat(struct filename *from, int newdfd,
+int do_symlinkat(struct filename *from, int newdfd, struct filename *to)
-		  struct filename *to)
 {
 	int error;
 	struct dentry *dentry;

include/uapi/linux/io_uring.h

@@ -134,6 +134,7 @@ enum {
 	IORING_OP_RENAMEAT,
 	IORING_OP_UNLINKAT,
 	IORING_OP_MKDIRAT,
+	IORING_OP_SYMLINKAT,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,