io_uring: support 0 length iov in buffer select in compat

Match up work done in "io_uring: allow iov_len = 0 for recvmsg and buffer
select", but for compat code path.

Fixes: a68caad69ce5 ("io_uring: allow iov_len = 0 for recvmsg and buffer select")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220708181838.1495428-3-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/net.c b/io_uring/net.c
index eb939899e9c5a08deb843719574cc99bb100fa3f..dc9190eafbe703ae7ac2779d05bfe9228bfddbb3 100644 (file)
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -382,16 +382,21 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
        if (req->flags & REQ_F_BUFFER_SELECT) {
                compat_ssize_t clen;
 
-               if (len > 1)
-                       return -EINVAL;
-               if (!access_ok(uiov, sizeof(*uiov)))
-                       return -EFAULT;
-               if (__get_user(clen, &uiov->iov_len))
-                       return -EFAULT;
-               if (clen < 0)
+               if (len == 0) {
+                       sr->len = 0;
+                       iomsg->free_iov = NULL;
+               } else if (len > 1) {
                        return -EINVAL;
-               sr->len = clen;
-               iomsg->free_iov = NULL;
+               } else {
+                       if (!access_ok(uiov, sizeof(*uiov)))
+                               return -EFAULT;
+                       if (__get_user(clen, &uiov->iov_len))
+                               return -EFAULT;
+                       if (clen < 0)
+                               return -EINVAL;
+                       sr->len = clen;
+                       iomsg->free_iov = NULL;
+               }
        } else {
                iomsg->free_iov = iomsg->fast_iov;
                ret = __import_iovec(READ, (struct iovec __user *)uiov, len,