vhost: make sure log_num < in_num

The code assumes log_num < in_num everywhere, and that is true as long as
in_num is incremented by descriptor iov count, and log_num by 1. However
this breaks if there's a zero sized descriptor.

As a result, if a malicious guest creates a vring desc with desc.len = 0,
it may cause the host kernel to crash by overflowing the log array. This
bug can be triggered during the VM migration.

There's no need to log when desc.len = 0, so just don't increment log_num
in this case.

Fixes: 3a4d5c94e959 ("vhost_net: a kernel-level virtio server")
Cc: [email protected]
Reviewed-by: Lidong Chen <[email protected]>
Signed-off-by: ruippan <[email protected]>
Signed-off-by: yongduan <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Tyler Hicks <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>

0 files changed, 0 insertions, 0 deletions