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@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>

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 8a329556f8dff389b646241d2cb1f48e8aacfd62..52b636d00a6b23bdfd6d62e04ebc87ff3f4db8db 100644 (file)
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -44,7 +44,7 @@ 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 += this_len;
+                       buf->addr = READ_ONCE(buf->addr) + this_len;
                        buf->len = buf_len;
                        return false;
                }
@@ -198,9 +198,9 @@ static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *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);
@@ -280,7 +280,7 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
        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);
 
@@ -295,7 +295,7 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
                        }
                }
 
-               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++;