[PATCH v2 for-next] io_uring/kbuf: validate ring provided buffer addresses with access_ok()

[Jens Axboe <axboe@kernel.dk>]

Commit:

809b997a5ce9 ("x86-64/arm64/powerpc: clean up and rename __copy_from_user_flushcache")

sanitized that any provided copy helper should separately validate
destination and source addresses, but we should also ensure that
anything that is retrieved from a buffer is validated upfront. For ring
provided buffers, always include an access_ok() when grabbing a new
buffer.

Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

v2: send actual patch, not an old version...

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 7a1c65f631c2..b9f4720ca22f 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -210,10 +210,14 @@ static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
 	buf_len = READ_ONCE(buf->len);
 	if (*len == 0 || *len > buf_len)
 		*len = buf_len;
+	sel.addr = u64_to_user_ptr(READ_ONCE(buf->addr));
+	if (unlikely(!access_ok(sel.addr, *len))) {
+		sel.addr = NULL;
+		return sel;
+	}
 	req->flags |= REQ_F_BUFFER_RING | REQ_F_BUFFERS_COMMIT;
 	req->buf_index = READ_ONCE(buf->bid);
 	sel.buf_list = bl;
-	sel.addr = u64_to_user_ptr(READ_ONCE(buf->addr));
 
 	if (io_should_commit(req, issue_flags)) {
 		if (!io_kbuf_commit(req, sel.buf_list, *len, 1))
@@ -250,6 +254,7 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 				struct io_buffer_list *bl)
 {
 	struct io_uring_buf_ring *br = bl->buf_ring;
+	struct iovec *org_iovs = arg->iovs;
 	struct iovec *iov = arg->iovs;
 	int nr_iovs = arg->nr_iovs;
 	__u16 nr_avail, tail, head;
@@ -311,6 +316,11 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 
 		iov->iov_base = u64_to_user_ptr(READ_ONCE(buf->addr));
 		iov->iov_len = len;
+		if (unlikely(!access_ok(iov->iov_base, len))) {
+			if (arg->iovs != org_iovs)
+				kfree(arg->iovs);
+			return -EFAULT;
+		}
 		iov++;
 
 		arg->out_len += len;
-- 
Jens Axboe