# \[PATCH AUTOSEL 4.19 04/10\] vringh: Use wiov-\>used to check for read/write desc order - From: Sasha Levin \ - Date: 2021-08-24 01:00:21 - List: virtualization - Page: https://ratatoskr.run/virtualization/2021/08/1486397 - Thread: https://ratatoskr.run/stable/2021/08/1486396/t.md ```text From: Neeraj Upadhyay [ Upstream commit e74cfa91f42c50f7f649b0eca46aa049754ccdbd ] As __vringh_iov() traverses a descriptor chain, it populates each descriptor entry into either read or write vring iov and increments that iov's ->used member. So, as we iterate over a descriptor chain, at any point, (riov/wriov)->used value gives the number of descriptor enteries available, which are to be read or written by the device. As all read iovs must precede the write iovs, wiov->used should be zero when we are traversing a read descriptor. Current code checks for wiov->i, to figure out whether any previous entry in the current descriptor chain was a write descriptor. However, iov->i is only incremented, when these vring iovs are consumed, at a later point, and remain 0 in __vringh_iov(). So, correct the check for read and write descriptor order, to use wiov->used. Acked-by: Jason Wang Reviewed-by: Stefano Garzarella Signed-off-by: Neeraj Upadhyay Link: https://lore.kernel.org/r/1624591502-4827-1-git-send-email-neeraju@codeaurora.org Signed-off-by: Michael S. Tsirkin Signed-off-by: Sasha Levin --- drivers/vhost/vringh.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c index 59c61744dcc1..97aa9b87e572 100644 --- a/drivers/vhost/vringh.c +++ b/drivers/vhost/vringh.c @@ -330,7 +330,7 @@ __vringh_iov(struct vringh *vrh, u16 i, iov = wiov; else { iov = riov; - if (unlikely(wiov && wiov->i)) { + if (unlikely(wiov && wiov->used)) { vringh_bad("Readable desc %p after writable", &descs[i]); err = -EINVAL; -- 2.30.2 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization ```