Re: [PATCH v2] net: parsing IFLA_INET_CONF broken since 7.1 if NLA_F_NESTED not set

[Ido Schimmel <idosch@nvidia.com>]

On Mon, Sep 14, 2026 at 08:02:07PM +0100, Quentin Armitage wrote:
> Commit fa8fca88714c ("ipv4: validate IPV4_DEVCONF attributes properly") changed
> inet_validate_link_af() to call nla_parse_nested() rather than
> nla_for_each_nested() for IFLA_INET_CONF. A side effect of this change is that
> the code now checks that NLA_F_NESTED is set for IFLA_INET_CONF, and rejects the
> message if it is not, whereas previously there was no check for NLA_F_NESTED
> being set.
> 
> The consequence of this is that code which worked prior to Linux 7.1, albeit
> erroneously not setting NLA_F_NESTED now fails.
> 
> In order to maintain backward compatibility, rather than calling
> nla_parse_nested(), nla_parse() is called.
> 
> From 498a8cffcdbbc3265d2a4747ba5ded6f562af3a7 Mon Sep 17 00:00:00 2001
> From: Quentin Armitage <quentin@armitage.org.uk>
> Date: Mon, 14 Sep 2026 18:19:53 +0100
> Subject: [PATCH v2] net: allow IFLA_INET_CONF messages when NLA_F_NESTED unset
> 
> Commit fa8fca88714c ("ipv4: validate IPV4_DEVCONF attributes properly")
> added validation of IFLA_INET_CONF attributes, and in the process
> changed the call of nla_for_each_nested() to nla_parse_nested(). A
> side effect of this change is that the IFLA_INET_CONF option is now
> tested for NLA_F_NESTED being set, and fails if it is not. Prior to the
> commit there was no check of NLA_F_NESTED.
> 
> Change nla_parse_nested() to nla_parse(). This restores the previous
> functionality of not checking NLA_F_NESTED, thereby allowing code that
> (incorrectly) doesn't set NLA_F_NESTED to continue to work.
> 
> Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>

1. The code looks fine, but the patch is corrupted and cannot be
applied:

$ b4 shazam 24158a1c7c9d7fc28d42a0be53f3b9d1919caa1b.camel@armitage.org.uk
[...]
Applying: net: parsing IFLA_INET_CONF broken since 7.1 if NLA_F_NESTED not set
Patch failed at 0001 net: parsing IFLA_INET_CONF broken since 7.1 if NLA_F_NESTED not set
error: corrupt patch at /home/idosch/code/linux/.git/rebase-apply/patch:10

2. Missing a Fixes tag just above your SoB:

Fixes: fa8fca88714c ("ipv4: validate IPV4_DEVCONF attributes properly")

3. Since Jakub asked, please mention in the commit message that this
change broke keepalived.

4. See more info about how to correctly format a patch here:

https://docs.kernel.org/next/process/maintainer-netdev.html
https://docs.kernel.org/next/process/submitting-patches.html