[PATCH v1] io_uring/kbuf: use WRITE_ONCE() for userspace-shared buffer ring fields

[Joanne Koong <joannelkoong@gmail.com>]

buf->addr and buf->len reside in memory shared with userspace. They
should be written with WRITE_ONCE() to guarantee atomic stores and
prevent tearing or other unsafe compiler optimizations.

Fixes: ae98dbf43d75 ("io_uring/kbuf: add support for incremental buffer consumption")
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Cc: Caleb Sander Mateos <csander@purestorage.com>
---
 io_uring/kbuf.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 52b636d00a6b..796d131107dd 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -44,11 +44,11 @@ static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 		buf_len -= this_len;
 		/* Stop looping for invalid buffer length of 0 */
 		if (buf_len || !this_len) {
-			buf->addr = READ_ONCE(buf->addr) + this_len;
-			buf->len = buf_len;
+			WRITE_ONCE(buf->addr, READ_ONCE(buf->addr) + this_len);
+			WRITE_ONCE(buf->len, buf_len);
 			return false;
 		}
-		buf->len = 0;
+		WRITE_ONCE(buf->len, 0);
 		bl->head++;
 		len -= this_len;
 	}
@@ -291,7 +291,7 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 				arg->partial_map = 1;
 				if (iov != arg->iovs)
 					break;
-				buf->len = len;
+				WRITE_ONCE(buf->len, len);
 			}
 		}
 
-- 
2.47.3