linux-kernel - RE: netlink getsockopt() sets only one byte?

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Message-ID: <0c2ea86d55454b55a88db716f967dda4@AcuMS.aculab.com>
Date:   Wed, 19 Apr 2023 15:43:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Brad Spencer' <bspencer@...ckberry.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: netlink getsockopt() sets only one byte?

From: Brad Spencer <bspencer@...ckberry.com>
> Sent: 18 April 2023 18:38
> 
> Calling getsockopt() on a netlink socket with SOL_NETLINK options that
> use type int only sets the first byte of the int value but returns an
> optlen equal to sizeof(int), at least on x86_64.
> 
> 
> The detailed description:
> 
> It looks like netlink_getsockopt() calls put_user() with a char*
> pointer, and I think that causes it to copy only one byte from the val
> result, despite len being sizeof(int).
> 
> Is this the expected behaviour?  The returned size is 4, after all,
> and other int-sized socket options (outside of netlink) like
> SO_REUSEADDR set all bytes of the int.

It will be horribly broken on anything big-endian.

	David

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