AliExpress is an online mall. You'll purchase from an individual store within that mall, and any warranty on the cameras will be set by whoever runs whichever store that you buy from.
We're pretty lucky here in that someone who runs an Ali store is an active member on the forum. His name is Andy, and his forum screen name is
@EMPIRETECANDY. He resells the unbranded Dahua products, which is the same quality product, just minus the logo being printed on it.
The URL to his Ali store is:
Empire Technology Co., Ltd - Small Orders Online Store, Hot Selling and more on Aliexpress.com | Alibaba Group
In regards to tech support, for Dahua stuff, the forum here has a wealth of info already posted, and you're always free to start a new thread. The few times issues have come up that the forum hasn't been able to solve, Andy's helped out by forwarding them over to Dahua support.
In regards to warranty, check what's stated in the product description on his store. I think it's one year.