[PATCH 5.8] io_uring: fix recvmsg selected buf leak

[Pavel Begunkov <asml.silence@gmail.com>]

io_recvmsg() doesn't free memory allocated for struct io_buffer.
Fix it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

1. This one is ugly, but automatically mergeable.
I have a half prepared set for-5.9.

2. to reproduce run
sudo sh -c 'for i in $(seq 1 100000000); do ./send_recvmsg; done'

and look for growing "kmalloc-32" slab
p.s. test(1, 0) in send_recvmsg.c is the one leaking

 fs/io_uring.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 9fd7e69696c3..74bc4a04befa 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3845,10 +3845,16 @@ static int io_recvmsg(struct io_kiocb *req, bool force_nonblock)
 
 		ret = __sys_recvmsg_sock(sock, &kmsg->msg, req->sr_msg.msg,
 						kmsg->uaddr, flags);
-		if (force_nonblock && ret == -EAGAIN)
-			return io_setup_async_msg(req, kmsg);
+		if (force_nonblock && ret == -EAGAIN) {
+			ret = io_setup_async_msg(req, kmsg);
+			if (ret != -EAGAIN)
+				kfree(kbuf);
+			return ret;
+		}
 		if (ret == -ERESTARTSYS)
 			ret = -EINTR;
+		if (kbuf)
+			kfree(kbuf);
 	}
 
 	if (kmsg && kmsg->iov != kmsg->fast_iov)
-- 
2.24.0