[PATCH 6.12 023/242] io_uring/kbuf: use WRITE_ONCE() for userspace-shared buffer ring fields

Greg Kroah-Hartman
2026-04-08T18:40:16Z

From: Joanne Koong <joannelkoong@gmail.com>

Commit a4c694bfc2455e82b7caf6045ca893d123e0ed11 upstream.

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.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Cc: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/kbuf.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -44,11 +44,11 @@ static bool io_kbuf_inc_commit(struct io
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;
}
@@ -289,7 +289,7 @@ static int io_ring_buffers_peek(struct i
arg->partial_map = 1;
if (iov != arg->iovs)
break;
- buf->len = len;
+ WRITE_ONCE(buf->len, len);
}
}