From 0b6d253e084a97a05f4970dee06d9a75d29a7bda Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 12 Sep 2024 09:29:29 -0600
Subject: [PATCH] io_uring/register: provide helper to get io_ring_ctx from
 'fd'

Can be done in one of two ways:

1) Regular file descriptor, just fget()
2) Registered ring, index our own table for that

In preparation for adding another register use of needing to get a ctx
from a file descriptor, abstract out this helper and use it in the main
register syscall as well.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/register.c | 58 +++++++++++++++++++++++++++------------------
 io_uring/register.h |  1 +
 2 files changed, 36 insertions(+), 23 deletions(-)

diff --git a/io_uring/register.c b/io_uring/register.c
index 57cb85c42526..d90159478045 100644
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -550,6 +550,38 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 	return ret;
 }
 
+/*
+ * Given an 'fd' value, return the ctx associated with if. If 'registered' is
+ * true, then the registered index is used. Otherwise, the normal fd table.
+ * Caller must call fput() on the returned file, unless it's an ERR_PTR.
+ */
+struct file *io_uring_register_get_file(int fd, bool registered)
+{
+	struct file *file;
+
+	if (registered) {
+		/*
+		 * Ring fd has been registered via IORING_REGISTER_RING_FDS, we
+		 * need only dereference our task private array to find it.
+		 */
+		struct io_uring_task *tctx = current->io_uring;
+
+		if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
+			return ERR_PTR(-EINVAL);
+		fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
+		file = tctx->registered_rings[fd];
+	} else {
+		file = fget(fd);
+	}
+
+	if (unlikely(!file))
+		return ERR_PTR(-EBADF);
+	if (io_is_uring_fops(file))
+		return file;
+	fput(file);
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
 SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
 		void __user *, arg, unsigned int, nr_args)
 {
@@ -564,35 +596,15 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
 	if (opcode >= IORING_REGISTER_LAST)
 		return -EINVAL;
 
-	if (use_registered_ring) {
-		/*
-		 * Ring fd has been registered via IORING_REGISTER_RING_FDS, we
-		 * need only dereference our task private array to find it.
-		 */
-		struct io_uring_task *tctx = current->io_uring;
-
-		if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
-			return -EINVAL;
-		fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
-		file = tctx->registered_rings[fd];
-		if (unlikely(!file))
-			return -EBADF;
-	} else {
-		file = fget(fd);
-		if (unlikely(!file))
-			return -EBADF;
-		ret = -EOPNOTSUPP;
-		if (!io_is_uring_fops(file))
-			goto out_fput;
-	}
-
+	file = io_uring_register_get_file(fd, use_registered_ring);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
 	ctx = file->private_data;
 
 	mutex_lock(&ctx->uring_lock);
 	ret = __io_uring_register(ctx, opcode, arg, nr_args);
 	mutex_unlock(&ctx->uring_lock);
 	trace_io_uring_register(ctx, opcode, ctx->nr_user_files, ctx->nr_user_bufs, ret);
-out_fput:
 	if (!use_registered_ring)
 		fput(file);
 	return ret;
diff --git a/io_uring/register.h b/io_uring/register.h
index c9da997d503c..cc69b88338fe 100644
--- a/io_uring/register.h
+++ b/io_uring/register.h
@@ -4,5 +4,6 @@
 
 int io_eventfd_unregister(struct io_ring_ctx *ctx);
 int io_unregister_personality(struct io_ring_ctx *ctx, unsigned id);
+struct file *io_uring_register_get_file(int fd, bool registered);
 
 #endif