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([2a0b:e7c0:0:107::49]) by smtp.gmail.com with ESMTPSA id qk30sm4393503ejb.125.2020.07.30.06.38.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jul 2020 06:38:07 -0700 (PDT) Subject: Re: [PATCH] vgacon: Fix an out-of-bounds in vgacon_scrollback_update() To: Yang Yingliang , b.zolnierkie@samsung.com Cc: dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?B?5byg5LqR5rW3?= References: <20200713105730.550334-1-yangyingliang@huawei.com> <220220f1-48f7-46f6-952f-ab41fa57d6a1@kernel.org> From: Jiri Slaby Message-ID: <9aecd7ac-5060-6b8d-61f8-393431eb243f@kernel.org> Date: Thu, 30 Jul 2020 15:38:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=iso-8859-2 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30. 07. 20, 15:24, Yang Yingliang wrote: > > On 2020/7/30 19:04, Jiri Slaby wrote: >> On 13. 07. 20, 12:57, Yang Yingliang wrote: >>> I got a slab-out-of-bounds report when I doing fuzz test. >>> >>> [  334.989515] >>> ================================================================== >>> [  334.989577] BUG: KASAN: slab-out-of-bounds in >>> vgacon_scroll+0x57a/0x8ed >>> [  334.989588] Write of size 1766 at addr ffff8883de69ff3e by task >>> test/2658 >>> [  334.989593] >>> [  334.989608] CPU: 3 PID: 2658 Comm: test Not tainted >>> 5.7.0-rc5-00005-g152036d1379f #789 >>> [  334.989617] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), >>> BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014 >>> [  334.989624] Call Trace: >>> [  334.989646]  dump_stack+0xe4/0x14e >>> [  334.989676]  print_address_description.constprop.5+0x3f/0x60 >>> [  334.989699]  ? vgacon_scroll+0x57a/0x8ed >>> [  334.989710]  __kasan_report.cold.8+0x92/0xaf >>> [  334.989735]  ? vgacon_scroll+0x57a/0x8ed >>> [  334.989761]  kasan_report+0x37/0x50 >>> [  334.989789]  check_memory_region+0x1c1/0x1e0 >>> [  334.989806]  memcpy+0x38/0x60 >>> [  334.989824]  vgacon_scroll+0x57a/0x8ed >>> [  334.989876]  con_scroll+0x4ef/0x5e0 >> ... >>> Because vgacon_scrollback_cur->tail plus memcpy size is greater than >>> vgacon_scrollback_cur->size. Fix this by checking the memcpy size. >>> >>> Reported-by: Hulk Robot >>> Signed-off-by: Yang Yingliang >>> --- >>>   drivers/video/console/vgacon.c | 11 ++++++++--- >>>   1 file changed, 8 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/video/console/vgacon.c >>> b/drivers/video/console/vgacon.c >>> index 998b0de1812f..b51ffb9a208d 100644 >>> --- a/drivers/video/console/vgacon.c >>> +++ b/drivers/video/console/vgacon.c >>> @@ -243,6 +243,7 @@ static void vgacon_scrollback_startup(void) >>>   static void vgacon_scrollback_update(struct vc_data *c, int t, int >>> count) >>>   { >>>       void *p; >>> +    int size; >>>         if (!vgacon_scrollback_cur->data || >>> !vgacon_scrollback_cur->size || >>>           c->vc_num != fg_console) >>> @@ -251,13 +252,17 @@ static void vgacon_scrollback_update(struct >>> vc_data *c, int t, int count) >>>       p = (void *) (c->vc_origin + t * c->vc_size_row); >>>         while (count--) { >>> +        size = vgacon_scrollback_cur->size - >>> vgacon_scrollback_cur->tail; >>> +        if (size > c->vc_size_row) >>> +            size = c->vc_size_row; >>> + >>>           scr_memcpyw(vgacon_scrollback_cur->data + >>>                   vgacon_scrollback_cur->tail, >>> -                p, c->vc_size_row); >>> +                p, size); >> Are you sure the consumer can handle split lines? As vgacon_scrolldelta >> (soff in particular) looks to me like it doesn't. >> >> Have you tested you patch? I mean with soft scrollback on the vga >> console? > > I only test the patch with the reproduce program. Out of curiosity, what is it doing? Resize and then scroll by \n (line feed)? Can you share it? thanks, -- js