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Date: Mon, 25 Jan 2016 16:12:01 +0000
From: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Daniel Vetter <daniel.vetter@ffwll.ch>,
        David Herrmann <dh.herrmann@gmail.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Imre Deak <imre.deak@intel.com>,
        "Lad, Prabhakar" <prabhakar.csengg@gmail.com>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Nicholas Mc Guire <hofrat@osadl.org>,
        Scot Doyle <lkml14@scotdoyle.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Takashi Iwai <tiwai@suse.de>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
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        Sasha Levin <sasha.levin@oracle.com>
Subject: Re: tty: kmalloc size WARNING in vc_do_resize
Message-ID: <20160125161201.5bf22992@lxorguk.ukuu.org.uk>
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> I think that either the kmalloc should use __GFP_NOWARN or
> vc_do_resize should do stricter size check.

vc_do_resize doesn't know enough to do a stricter size check. There are
not many methods it calls but those are:

vgacon_resize doesn't error when stupid things happen because of a silly
hack for legacy svgatextmode tools.

sisusbcon_resize does the right checks but we can get in a situation
where we unplug during a resize so attempting to resize and size back
might fail.

fbcon_resize does the right thing, but again can error if we go
size/resize/size back.

That means we really have to guess or would have to add 'max size' info
the structures. Right now it's clamped to 1Gbyte which is a 32767 x 32767
character display and probably ludicrous. Clamping to 4048 x 1024 chars
would cover displays up to 16K x 6K even with the 4x6 font (which is
insane on a 4K display, let alone 4 of them).

Alan