netdev - Re: [PATCH] can: bcm: fix infoleak in struct bcm_msg

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Date:   Sun, 13 Jun 2021 20:33:31 +0200
From:   Norbert Slusarek <nslusarek@....net>
To:     Patrick Menschel <menschel.p@...teo.de>
Cc:     Oliver Hartkopp <socketcan@...tkopp.net>, mkl@...gutronix.de,
        davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] can: bcm: fix infoleak in struct bcm_msg_head

>Ouch,
>
>I should not skip lines while reading.
>We're talking about different gaps as it seems. I didn't realize the gap
>in front of ival1 before.
>
>There is also a gap in between nframes and frames[0].
>That one is caused by align(8) of data in struct can_frame.
>It propagates upwards into that gap on 32bit arch.
>You can find it if you actually fill frames[] with a frame.
>
>I found it while concatenating bcm_msg_head and a can frame into a
>python bytearray which was too short for the raspberry pi as I forgot
>the alignment.
>
>I came up with a format string "IIIllllII0q" for bcm_msg_head.
>
>Kind Regards,
>Patrick

I confirm that there is a similar 4-byte leak happening on 32-bit systems.
It's possible to retrieve kernel addresses etc. which allows for a KASLR
bypass. I will request a CVE and publish a notice regarding
this on oss-security where I will mention Patrick too.

Anyways, this patch seems to be working for the leak on 32-bit systems as well.

Norbert