linux-kernel - [PATCH 5/7] eventpoll: move file checking earlier for epoll

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Date:   Thu,  1 Dec 2022 11:11:54 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc:     soheil@...gle.com, willemdebruijn.kernel@...il.com,
        stefanha@...hat.com, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5/7] eventpoll: move file checking earlier for epoll_ctl()

This just cleans up the checking a bit, in preparation for a change
that will need access to 'ep' earlier.

Signed-off-by: Jens Axboe <axboe@...nel.dk>
---
 fs/eventpoll.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 0994f2eb6adc..962d897bbfc6 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2111,6 +2111,20 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 	if (!f.file)
 		goto error_return;
 
+	/*
+	 * We have to check that the file structure underneath the file
+	 * descriptor the user passed to us _is_ an eventpoll file.
+	 */
+	error = -EINVAL;
+	if (!is_file_epoll(f.file))
+		goto error_fput;
+
+	/*
+	 * At this point it is safe to assume that the "private_data" contains
+	 * our own data structure.
+	 */
+	ep = f.file->private_data;
+
 	/* Get the "struct file *" for the target file */
 	tf = fdget(fd);
 	if (!tf.file)
@@ -2126,12 +2140,10 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 		ep_take_care_of_epollwakeup(epds);
 
 	/*
-	 * We have to check that the file structure underneath the file descriptor
-	 * the user passed to us _is_ an eventpoll file. And also we do not permit
-	 * adding an epoll file descriptor inside itself.
+	 * We do not permit adding an epoll file descriptor inside itself.
 	 */
 	error = -EINVAL;
-	if (f.file == tf.file || !is_file_epoll(f.file))
+	if (f.file == tf.file)
 		goto error_tgt_fput;
 
 	/*
@@ -2147,12 +2159,6 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 			goto error_tgt_fput;
 	}
 
-	/*
-	 * At this point it is safe to assume that the "private_data" contains
-	 * our own data structure.
-	 */
-	ep = f.file->private_data;
-
 	/*
 	 * When we insert an epoll file descriptor inside another epoll file
 	 * descriptor, there is the chance of creating closed loops, which are
-- 
2.35.1