[PATCH 5.9 42/75] io_uring: fix recvmsg setup with compat buf-select

[Greg Kroah-Hartman]

From: Pavel Begunkov <asml.silence@xxxxxxxxx>

commit 2d280bc8930ba9ed1705cfd548c6c8924949eaf1 upstream.

__io_compat_recvmsg_copy_hdr() with REQ_F_BUFFER_SELECT reads out iov
len but never assigns it to iov/fast_iov, leaving sr->len with garbage.
Hopefully, following io_buffer_select() truncates it to the selected
buffer size, but the value is still may be under what was specified.

Cc: <stable@xxxxxxxxxxxxxxx> # 5.7
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/io_uring.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4300,7 +4300,8 @@ static int __io_compat_recvmsg_copy_hdr(
 			return -EFAULT;
 		if (clen < 0)
 			return -EINVAL;
-		sr->len = iomsg->iov[0].iov_len;
+		sr->len = clen;
+		iomsg->iov[0].iov_len = clen;
 		iomsg->iov = NULL;
 	} else {
 		ret = compat_import_iovec(READ, uiov, len, UIO_FASTIOV,