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From: "zhangxiaoxu (A)" <zhangxiaoxu5@huawei.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: akpm@osdl.org, pmladek@suse.com, wangkefeng.wang@huawei.com,
	b.zolnierkie@samsung.com, linux-fbdev@vger.kernel.org,
	dri-devel@lists.freedesktop.org, sergey.senozhatsky@gmail.com
Subject: Re: [PATCH] vgacon: Fix a UAF in vgacon_invert_region
Date: Tue, 03 Mar 2020 14:30:14 +0000	[thread overview]
Message-ID: <67073029-8477-5f5a-ed2a-bb5ad4896878@huawei.com> (raw)
In-Reply-To: <20200303135940.GS13686@intel.com>



在 2020/3/3 21:59, Ville Syrjälä 写道:
> That doesn't match how vc_screenbuf_size is computed elsewhere. Also
> a lot of places seem to assume that the screenbuf can be larger than
> vga_vram_size (eg. all the memcpy()s pick the smaller size of the
> two).
Yes, in the vga source code, we also pick the smaller size of two. But
in other place, eg: vc_do_resize, copy the old_origin to new_origin, we
not do that. It also make bad access happen. it maybe CVE-2020-8647.

I think we should just assume the width/height maybe larger than the
default, not the screenbuf larger than vga_vram_size.

If not, any useful of the larger screenbuf?

> 
> And you're changing the behaviour of the code when
> 'width % 2 && user' is true

WARNING: multiple messages have this Message-ID (diff)
From: "zhangxiaoxu (A)" <zhangxiaoxu5@huawei.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: akpm@osdl.org, pmladek@suse.com, wangkefeng.wang@huawei.com,
	b.zolnierkie@samsung.com, linux-fbdev@vger.kernel.org,
	dri-devel@lists.freedesktop.org, sergey.senozhatsky@gmail.com
Subject: Re: [PATCH] vgacon: Fix a UAF in vgacon_invert_region
Date: Tue, 3 Mar 2020 22:30:14 +0800	[thread overview]
Message-ID: <67073029-8477-5f5a-ed2a-bb5ad4896878@huawei.com> (raw)
In-Reply-To: <20200303135940.GS13686@intel.com>



在 2020/3/3 21:59, Ville Syrjälä 写道:
> That doesn't match how vc_screenbuf_size is computed elsewhere. Also
> a lot of places seem to assume that the screenbuf can be larger than
> vga_vram_size (eg. all the memcpy()s pick the smaller size of the
> two).
Yes, in the vga source code, we also pick the smaller size of two. But
in other place, eg: vc_do_resize, copy the old_origin to new_origin, we
not do that. It also make bad access happen. it maybe CVE-2020-8647.

I think we should just assume the width/height maybe larger than the
default, not the screenbuf larger than vga_vram_size.

If not, any useful of the larger screenbuf?

> 
> And you're changing the behaviour of the code when
> 'width % 2 && user' is true

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dri-devel@lists.freedesktop.org
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  reply	other threads:[~2020-03-03 14:30 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-03  3:20 [PATCH] vgacon: Fix a UAF in vgacon_invert_region Zhang Xiaoxu
2020-03-03  3:20 ` Zhang Xiaoxu
2020-03-03 13:59 ` Ville Syrjälä
2020-03-03 13:59   ` Ville Syrjälä
2020-03-03 14:30   ` zhangxiaoxu (A) [this message]
2020-03-03 14:30     ` zhangxiaoxu (A)
2020-03-03 14:46     ` Ville Syrjälä
2020-03-03 14:46       ` Ville Syrjälä
2020-03-04  1:31       ` zhangxiaoxu (A)
2020-03-04  1:31         ` zhangxiaoxu (A)

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