Re: [PATCH net v2] netlabel: validate unlabeled mask attribute length

[Jakub Kicinski <kuba@kernel.org>]

On Thu, 28 May 2026 09:59:13 +0800 Chenguang Zhao wrote:
> netlbl_unlabel_addrinfo_get() checked the address length
> but allowed shorter mask attributes to pass through to
> fixed-size address reads.
> 
> netlbl_unlabel_addrinfo_get() only rejected a mask
> length mismatch when the address attribute length
> was also invalid.  A crafted Generic Netlink request
> could therefore provide a valid IPv4/IPv6 address
> attribute with a shorter mask attribute.
> 
> NLA_BINARY policy lengths are maximum lengths,
> not exact lengths, so the short mask can pass
> policy validation.  The mask is later read as
> a full struct in_addr or struct in6_addr.
> Require both address and mask attributes to
> have the exact expected size.

Sorry, didn't look at this until Paul responded.

NLA_BINARY does _default_ to maximum lengths.
But you can use NLA_POLICY_EXACT_LEN() to have the policy do the right
thing. Using the policy is preferred - less code, and policy
introspection informs user space about the expectations.
-- 
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