linux-kernel - [PATCH] io_uring/kbuf: use READ_ONCE() for userspace-mapped memory

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Message-ID: <20251204224332.1181383-1-csander@purestorage.com>
Date: Thu,  4 Dec 2025 15:43:31 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: Caleb Sander Mateos <csander@...estorage.com>,
	Joanne Koong <joannelkoong@...il.com>,
	io-uring@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] io_uring/kbuf: use READ_ONCE() for userspace-mapped memory

The struct io_uring_buf elements in a buffer ring are in a memory region
accessible from userspace. A malicious/buggy userspace program could
therefore write to them at any time, so they should be accessed with
READ_ONCE() in the kernel. Commit 98b6fa62c84f ("io_uring/kbuf: always
use READ_ONCE() to read ring provided buffer lengths") already switched
the reads of the len field to READ_ONCE(). Do the same for bid and addr.

Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
Cc: Joanne Koong <joannelkoong@...il.com>
---
 io_uring/kbuf.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 8a329556f8df..52b636d00a6b 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -42,11 +42,11 @@ static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 		buf_len = READ_ONCE(buf->len);
 		this_len = min_t(u32, len, buf_len);
 		buf_len -= this_len;
 		/* Stop looping for invalid buffer length of 0 */
 		if (buf_len || !this_len) {
-			buf->addr += this_len;
+			buf->addr = READ_ONCE(buf->addr) + this_len;
 			buf->len = buf_len;
 			return false;
 		}
 		buf->len = 0;
 		bl->head++;
@@ -196,13 +196,13 @@ static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
 	buf = io_ring_head_to_buf(br, head, bl->mask);
 	buf_len = READ_ONCE(buf->len);
 	if (*len == 0 || *len > buf_len)
 		*len = buf_len;
 	req->flags |= REQ_F_BUFFER_RING | REQ_F_BUFFERS_COMMIT;
-	req->buf_index = buf->bid;
+	req->buf_index = READ_ONCE(buf->bid);
 	sel.buf_list = bl;
-	sel.addr = u64_to_user_ptr(buf->addr);
+	sel.addr = u64_to_user_ptr(READ_ONCE(buf->addr));
 
 	if (io_should_commit(req, issue_flags)) {
 		io_kbuf_commit(req, sel.buf_list, *len, 1);
 		sel.buf_list = NULL;
 	}
@@ -278,11 +278,11 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 
 	/* set it to max, if not set, so we can use it unconditionally */
 	if (!arg->max_len)
 		arg->max_len = INT_MAX;
 
-	req->buf_index = buf->bid;
+	req->buf_index = READ_ONCE(buf->bid);
 	do {
 		u32 len = READ_ONCE(buf->len);
 
 		/* truncate end piece, if needed, for non partial buffers */
 		if (len > arg->max_len) {
@@ -293,11 +293,11 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 					break;
 				buf->len = len;
 			}
 		}
 
-		iov->iov_base = u64_to_user_ptr(buf->addr);
+		iov->iov_base = u64_to_user_ptr(READ_ONCE(buf->addr));
 		iov->iov_len = len;
 		iov++;
 
 		arg->out_len += len;
 		arg->max_len -= len;
-- 
2.45.2