netdev - [PATCH v5 0/2] netlink: export policy on validation failures

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Date:   Thu,  8 Oct 2020 12:45:15 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     netdev@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH v5 0/2] netlink: export policy on validation failures

Export the policy used for attribute validation when it fails,
so e.g. for an out-of-range attribute userspace immediately gets
the valid ranges back.

v2 incorporates the suggestion from Jakub to have a function to
estimate the size (netlink_policy_dump_attr_size_estimate()) and
check that it does the right thing on the *normal* policy dumps,
not (just) when calling it from the error scenario.

v3 only addresses a few minor style issues.

v4 fixes up a forgotten 'git add' ... sorry.

v5 is a resend, I messed up v4's cover letter subject (saying v3)
and apparently the second patch didn't go out at all.

Tested using nl80211/iw in a few scenarios, seems to work fine
and return the policy back, e.g.

kernel reports: integer out of range
policy: 04 00 0b 00 0c 00 04 00 01 00 00 00 00 00 00 00 
        ^ padding
                    ^ minimum allowed value
policy: 04 00 0b 00 0c 00 05 00 ff ff ff ff 00 00 00 00 
        ^ padding
                    ^ maximum allowed value
policy: 08 00 01 00 04 00 00 00 
        ^ type 4 == U32

for an out-of-range case.

johannes