[PATCH 6.12 022/242] io_uring/kbuf: use READ_ONCE() for userspace-mapped memory

Greg Kroah-Hartman
2026-04-08T18:40:13Z

From: Caleb Sander Mateos <csander@purestorage.com>

Commit 78385c7299f7514697d196b3233a91bd5e485591 upstream.

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@purestorage.com>
Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
Cc: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/kbuf.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -44,7 +44,7 @@ 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 += this_len;
+ buf->addr = READ_ONCE(buf->addr) + this_len;
buf->len = buf_len;
return false;
}
@@ -185,9 +185,9 @@ static struct io_br_sel io_ring_buffer_s
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 (issue_flags & IO_URING_F_UNLOCKED || !io_file_can_poll(req)) {
/*
@@ -278,7 +278,7 @@ static int io_ring_buffers_peek(struct i
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);

@@ -293,7 +293,7 @@ static int io_ring_buffers_peek(struct i
}
}

- 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++;