From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98B9FC433E1 for ; Wed, 29 Jul 2020 07:02:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82E582070B for ; Wed, 29 Jul 2020 07:02:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727811AbgG2HCy (ORCPT ); Wed, 29 Jul 2020 03:02:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:37728 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726314AbgG2HCx (ORCPT ); Wed, 29 Jul 2020 03:02:53 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E8C71AB55; Wed, 29 Jul 2020 07:03:02 +0000 (UTC) From: Jiri Slaby To: b.zolnierkie@samsung.com Cc: linux-kernel@vger.kernel.org, Jiri Slaby , =?UTF-8?q?=E5=BC=A0=E4=BA=91=E6=B5=B7?= , Yang Yingliang , Kyungtae Kim , Linus Torvalds , Greg KH , Solar Designer , "Srivatsa S. Bhat" , Anthony Liguori , Security Officers , linux-distros@vs.openwall.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org Subject: [PATCH] vgacon: fix out of bounds write to the scrollback buffer Date: Wed, 29 Jul 2020 09:02:49 +0200 Message-Id: <20200729070249.20892-1-jslaby@suse.cz> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The current vgacon's scroll up implementation uses a circural buffer in vgacon_scrollback_cur. It always advances tail to prepare it for the next write and caps it to zero if the next ->vc_size_row bytes won't fit. But when we change the VT size (e.g. by VT_RESIZE) in the meantime, the new line might not fit to the end of the scrollback buffer in the next attempt to scroll. This leads to various crashes as vgacon_scrollback_update writes out of the buffer: BUG: unable to handle page fault for address: ffffc900001752a0 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page RIP: 0010:mutex_unlock+0x13/0x30 ... Call Trace: n_tty_write+0x1a0/0x4d0 tty_write+0x1a0/0x2e0 Or to KASAN reports: BUG: KASAN: slab-out-of-bounds in vgacon_scroll+0x57a/0x8ed So check whether the line fits in the buffer and wrap if needed. Do it before the loop as console_sem is held and ->vc_size_row cannot change during the execution of vgacon_scrollback_cur. If it does change, we need to ensure it does not change elsewhere, not here. Also, we do not split the write of a line into chunks as that would break the consumers of the buffer. They expect ->cnt, ->tail and ->size to be in harmony and advanced by ->vc_size_row. I found few reports of this in the past, some with patches included, some even 2 years old: https://lore.kernel.org/lkml/CAEAjamsJnG-=TSOwgRbbb3B9Z-PA63oWmNPoKYWQ=Z=+X49akg@mail.gmail.com/ https://lore.kernel.org/lkml/1589336932-35508-1-git-send-email-yangyingliang@huawei.com/ This fixes CVE-2020-14331. Big thanks to guys mentioned in the Reported-and-debugged-by lines below who actually found the root cause. Signed-off-by: Jiri Slaby Reported-and-debugged-by: 张云海 Reported-and-debugged-by: Yang Yingliang Reported-by: Kyungtae Kim Fixes: 15bdab959c9b ([PATCH] vgacon: Add support for soft scrollback) Cc: Linus Torvalds Cc: Greg KH Cc: Solar Designer Cc: "Srivatsa S. Bhat" Cc: Anthony Liguori Cc: Security Officers Cc: linux-distros@vs.openwall.org Cc: Yang Yingliang Cc: Bartlomiej Zolnierkiewicz Cc: dri-devel@lists.freedesktop.org Cc: linux-fbdev@vger.kernel.org --- drivers/video/console/vgacon.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index f0f3d573f848..13194bb246f8 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -250,6 +250,11 @@ static void vgacon_scrollback_update(struct vc_data *c, int t, int count) p = (void *) (c->vc_origin + t * c->vc_size_row); + /* vc_size_row might have changed by VT_RESIZE in the meantime */ + if ((vgacon_scrollback_cur->tail + c->vc_size_row) >= + vgacon_scrollback_cur->size) + vgacon_scrollback_cur->tail = 0; + while (count--) { scr_memcpyw(vgacon_scrollback_cur->data + vgacon_scrollback_cur->tail, -- 2.28.0 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Slaby Date: Wed, 29 Jul 2020 07:02:49 +0000 Subject: [PATCH] vgacon: fix out of bounds write to the scrollback buffer Message-Id: <20200729070249.20892-1-jslaby@suse.cz> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: b.zolnierkie@samsung.com Cc: Security Officers , Kyungtae Kim , Anthony Liguori , Jiri Slaby , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Srivatsa S. Bhat" , linux-distros@vs.openwall.org, linux-fbdev@vger.kernel.org, Greg KH , Solar Designer , Yang Yingliang , Linus Torvalds , =?UTF-8?q?=E5=BC=A0=E4=BA=91=E6=B5=B7?= The current vgacon's scroll up implementation uses a circural buffer in vgacon_scrollback_cur. It always advances tail to prepare it for the next write and caps it to zero if the next ->vc_size_row bytes won't fit. But when we change the VT size (e.g. by VT_RESIZE) in the meantime, the new line might not fit to the end of the scrollback buffer in the next attempt to scroll. This leads to various crashes as vgacon_scrollback_update writes out of the buffer: BUG: unable to handle page fault for address: ffffc900001752a0 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page RIP: 0010:mutex_unlock+0x13/0x30 ... Call Trace: n_tty_write+0x1a0/0x4d0 tty_write+0x1a0/0x2e0 Or to KASAN reports: BUG: KASAN: slab-out-of-bounds in vgacon_scroll+0x57a/0x8ed So check whether the line fits in the buffer and wrap if needed. Do it before the loop as console_sem is held and ->vc_size_row cannot change during the execution of vgacon_scrollback_cur. If it does change, we need to ensure it does not change elsewhere, not here. Also, we do not split the write of a line into chunks as that would break the consumers of the buffer. They expect ->cnt, ->tail and ->size to be in harmony and advanced by ->vc_size_row. I found few reports of this in the past, some with patches included, some even 2 years old: https://lore.kernel.org/lkml/CAEAjamsJnG-=TSOwgRbbb3B9Z-PA63oWmNPoKYWQ=Z=+X49akg@mail.gmail.com/ https://lore.kernel.org/lkml/1589336932-35508-1-git-send-email-yangyingliang@huawei.com/ This fixes CVE-2020-14331. Big thanks to guys mentioned in the Reported-and-debugged-by lines below who actually found the root cause. Signed-off-by: Jiri Slaby Reported-and-debugged-by: 张云海 Reported-and-debugged-by: Yang Yingliang Reported-by: Kyungtae Kim Fixes: 15bdab959c9b ([PATCH] vgacon: Add support for soft scrollback) Cc: Linus Torvalds Cc: Greg KH Cc: Solar Designer Cc: "Srivatsa S. Bhat" Cc: Anthony Liguori Cc: Security Officers Cc: linux-distros@vs.openwall.org Cc: Yang Yingliang Cc: Bartlomiej Zolnierkiewicz Cc: dri-devel@lists.freedesktop.org Cc: linux-fbdev@vger.kernel.org --- drivers/video/console/vgacon.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index f0f3d573f848..13194bb246f8 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -250,6 +250,11 @@ static void vgacon_scrollback_update(struct vc_data *c, int t, int count) p = (void *) (c->vc_origin + t * c->vc_size_row); + /* vc_size_row might have changed by VT_RESIZE in the meantime */ + if ((vgacon_scrollback_cur->tail + c->vc_size_row) >+ vgacon_scrollback_cur->size) + vgacon_scrollback_cur->tail = 0; + while (count--) { scr_memcpyw(vgacon_scrollback_cur->data + vgacon_scrollback_cur->tail, -- 2.28.0 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6207EC433E0 for ; Wed, 29 Jul 2020 07:02:55 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3EC7A2070B for ; Wed, 29 Jul 2020 07:02:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3EC7A2070B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 20D616E450; Wed, 29 Jul 2020 07:02:54 +0000 (UTC) Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by gabe.freedesktop.org (Postfix) with ESMTPS id D99D26E450 for ; Wed, 29 Jul 2020 07:02:52 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E8C71AB55; Wed, 29 Jul 2020 07:03:02 +0000 (UTC) From: Jiri Slaby To: b.zolnierkie@samsung.com Subject: [PATCH] vgacon: fix out of bounds write to the scrollback buffer Date: Wed, 29 Jul 2020 09:02:49 +0200 Message-Id: <20200729070249.20892-1-jslaby@suse.cz> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Security Officers , Kyungtae Kim , Anthony Liguori , Jiri Slaby , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Srivatsa S. Bhat" , linux-distros@vs.openwall.org, linux-fbdev@vger.kernel.org, Greg KH , Solar Designer , Yang Yingliang , Linus Torvalds , =?UTF-8?q?=E5=BC=A0=E4=BA=91=E6=B5=B7?= Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" VGhlIGN1cnJlbnQgdmdhY29uJ3Mgc2Nyb2xsIHVwIGltcGxlbWVudGF0aW9uIHVzZXMgYSBjaXJj dXJhbCBidWZmZXIKaW4gdmdhY29uX3Njcm9sbGJhY2tfY3VyLiBJdCBhbHdheXMgYWR2YW5jZXMg dGFpbCB0byBwcmVwYXJlIGl0IGZvciB0aGUKbmV4dCB3cml0ZSBhbmQgY2FwcyBpdCB0byB6ZXJv IGlmIHRoZSBuZXh0IC0+dmNfc2l6ZV9yb3cgYnl0ZXMgd29uJ3QgZml0LgoKQnV0IHdoZW4gd2Ug Y2hhbmdlIHRoZSBWVCBzaXplIChlLmcuIGJ5IFZUX1JFU0laRSkgaW4gdGhlIG1lYW50aW1lLCB0 aGUgbmV3CmxpbmUgbWlnaHQgbm90IGZpdCB0byB0aGUgZW5kIG9mIHRoZSBzY3JvbGxiYWNrIGJ1 ZmZlciBpbiB0aGUgbmV4dAphdHRlbXB0IHRvIHNjcm9sbC4gVGhpcyBsZWFkcyB0byB2YXJpb3Vz IGNyYXNoZXMgYXMKdmdhY29uX3Njcm9sbGJhY2tfdXBkYXRlIHdyaXRlcyBvdXQgb2YgdGhlIGJ1 ZmZlcjoKIEJVRzogdW5hYmxlIHRvIGhhbmRsZSBwYWdlIGZhdWx0IGZvciBhZGRyZXNzOiBmZmZm YzkwMDAwMTc1MmEwCiAjUEY6IHN1cGVydmlzb3Igd3JpdGUgYWNjZXNzIGluIGtlcm5lbCBtb2Rl CiAjUEY6IGVycm9yX2NvZGUoMHgwMDAyKSAtIG5vdC1wcmVzZW50IHBhZ2UKIFJJUDogMDAxMDpt dXRleF91bmxvY2srMHgxMy8weDMwCi4uLgogQ2FsbCBUcmFjZToKICBuX3R0eV93cml0ZSsweDFh MC8weDRkMAogIHR0eV93cml0ZSsweDFhMC8weDJlMAoKT3IgdG8gS0FTQU4gcmVwb3J0czoKQlVH OiBLQVNBTjogc2xhYi1vdXQtb2YtYm91bmRzIGluIHZnYWNvbl9zY3JvbGwrMHg1N2EvMHg4ZWQK ClNvIGNoZWNrIHdoZXRoZXIgdGhlIGxpbmUgZml0cyBpbiB0aGUgYnVmZmVyIGFuZCB3cmFwIGlm IG5lZWRlZC4gRG8gaXQKYmVmb3JlIHRoZSBsb29wIGFzIGNvbnNvbGVfc2VtIGlzIGhlbGQgYW5k IC0+dmNfc2l6ZV9yb3cgY2Fubm90IGNoYW5nZQpkdXJpbmcgdGhlIGV4ZWN1dGlvbiBvZiB2Z2Fj b25fc2Nyb2xsYmFja19jdXIuIElmIGl0IGRvZXMgY2hhbmdlLCB3ZQpuZWVkIHRvIGVuc3VyZSBp dCBkb2VzIG5vdCBjaGFuZ2UgZWxzZXdoZXJlLCBub3QgaGVyZS4KCkFsc28sIHdlIGRvIG5vdCBz cGxpdCB0aGUgd3JpdGUgb2YgYSBsaW5lIGludG8gY2h1bmtzIGFzIHRoYXQgd291bGQKYnJlYWsg dGhlIGNvbnN1bWVycyBvZiB0aGUgYnVmZmVyLiBUaGV5IGV4cGVjdCAtPmNudCwgLT50YWlsIGFu ZCAtPnNpemUKdG8gYmUgaW4gaGFybW9ueSBhbmQgYWR2YW5jZWQgYnkgLT52Y19zaXplX3Jvdy4K CkkgZm91bmQgZmV3IHJlcG9ydHMgb2YgdGhpcyBpbiB0aGUgcGFzdCwgc29tZSB3aXRoIHBhdGNo ZXMgaW5jbHVkZWQsCnNvbWUgZXZlbiAyIHllYXJzIG9sZDoKaHR0cHM6Ly9sb3JlLmtlcm5lbC5v cmcvbGttbC9DQUVBamFtc0puRy09VFNPd2dSYmJiM0I5Wi1QQTYzb1dtTlBvS1lXUT1aPStYNDlh a2dAbWFpbC5nbWFpbC5jb20vCmh0dHBzOi8vbG9yZS5rZXJuZWwub3JnL2xrbWwvMTU4OTMzNjkz Mi0zNTUwOC0xLWdpdC1zZW5kLWVtYWlsLXlhbmd5aW5nbGlhbmdAaHVhd2VpLmNvbS8KClRoaXMg Zml4ZXMgQ1ZFLTIwMjAtMTQzMzEuCgpCaWcgdGhhbmtzIHRvIGd1eXMgbWVudGlvbmVkIGluIHRo ZSBSZXBvcnRlZC1hbmQtZGVidWdnZWQtYnkgbGluZXMgYmVsb3cKd2hvIGFjdHVhbGx5IGZvdW5k IHRoZSByb290IGNhdXNlLgoKU2lnbmVkLW9mZi1ieTogSmlyaSBTbGFieSA8anNsYWJ5QHN1c2Uu Y3o+ClJlcG9ydGVkLWFuZC1kZWJ1Z2dlZC1ieTog5byg5LqR5rW3IDx6aGFuZ3l1bmhhaUBuc2Zv Y3VzLmNvbT4KUmVwb3J0ZWQtYW5kLWRlYnVnZ2VkLWJ5OiBZYW5nIFlpbmdsaWFuZyA8eWFuZ3lp bmdsaWFuZ0BodWF3ZWkuY29tPgpSZXBvcnRlZC1ieTogS3l1bmd0YWUgS2ltIDxrdDA3NTVAZ21h aWwuY29tPgpGaXhlczogMTViZGFiOTU5YzliIChbUEFUQ0hdIHZnYWNvbjogQWRkIHN1cHBvcnQg Zm9yIHNvZnQgc2Nyb2xsYmFjaykKQ2M6IExpbnVzIFRvcnZhbGRzIDx0b3J2YWxkc0BsaW51eC1m b3VuZGF0aW9uLm9yZz4KQ2M6IEdyZWcgS0ggPGdyZWdAa3JvYWguY29tPgpDYzogU29sYXIgRGVz aWduZXIgPHNvbGFyQG9wZW53YWxsLmNvbT4KQ2M6ICJTcml2YXRzYSBTLiBCaGF0IiA8c3JpdmF0 c2FAY3NhaWwubWl0LmVkdT4KQ2M6IEFudGhvbnkgTGlndW9yaSA8YWxpZ3VvcmlAYW1hem9uLmNv bT4KQ2M6IFNlY3VyaXR5IE9mZmljZXJzIDxzZWN1cml0eUBrZXJuZWwub3JnPgpDYzogbGludXgt ZGlzdHJvc0B2cy5vcGVud2FsbC5vcmcKQ2M6IFlhbmcgWWluZ2xpYW5nIDx5YW5neWluZ2xpYW5n QGh1YXdlaS5jb20+CkNjOiBCYXJ0bG9taWVqIFpvbG5pZXJraWV3aWN6IDxiLnpvbG5pZXJraWVA c2Ftc3VuZy5jb20+CkNjOiBkcmktZGV2ZWxAbGlzdHMuZnJlZWRlc2t0b3Aub3JnCkNjOiBsaW51 eC1mYmRldkB2Z2VyLmtlcm5lbC5vcmcKLS0tCiBkcml2ZXJzL3ZpZGVvL2NvbnNvbGUvdmdhY29u LmMgfCA1ICsrKysrCiAxIGZpbGUgY2hhbmdlZCwgNSBpbnNlcnRpb25zKCspCgpkaWZmIC0tZ2l0 IGEvZHJpdmVycy92aWRlby9jb25zb2xlL3ZnYWNvbi5jIGIvZHJpdmVycy92aWRlby9jb25zb2xl L3ZnYWNvbi5jCmluZGV4IGYwZjNkNTczZjg0OC4uMTMxOTRiYjI0NmY4IDEwMDY0NAotLS0gYS9k cml2ZXJzL3ZpZGVvL2NvbnNvbGUvdmdhY29uLmMKKysrIGIvZHJpdmVycy92aWRlby9jb25zb2xl L3ZnYWNvbi5jCkBAIC0yNTAsNiArMjUwLDExIEBAIHN0YXRpYyB2b2lkIHZnYWNvbl9zY3JvbGxi YWNrX3VwZGF0ZShzdHJ1Y3QgdmNfZGF0YSAqYywgaW50IHQsIGludCBjb3VudCkKIAogCXAgPSAo dm9pZCAqKSAoYy0+dmNfb3JpZ2luICsgdCAqIGMtPnZjX3NpemVfcm93KTsKIAorCS8qIHZjX3Np emVfcm93IG1pZ2h0IGhhdmUgY2hhbmdlZCBieSBWVF9SRVNJWkUgaW4gdGhlIG1lYW50aW1lICov CisJaWYgKCh2Z2Fjb25fc2Nyb2xsYmFja19jdXItPnRhaWwgKyBjLT52Y19zaXplX3JvdykgPj0K KwkJCXZnYWNvbl9zY3JvbGxiYWNrX2N1ci0+c2l6ZSkKKwkJdmdhY29uX3Njcm9sbGJhY2tfY3Vy LT50YWlsID0gMDsKKwogCXdoaWxlIChjb3VudC0tKSB7CiAJCXNjcl9tZW1jcHl3KHZnYWNvbl9z Y3JvbGxiYWNrX2N1ci0+ZGF0YSArCiAJCQkgICAgdmdhY29uX3Njcm9sbGJhY2tfY3VyLT50YWls LAotLSAKMi4yOC4wCgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fXwpkcmktZGV2ZWwgbWFpbGluZyBsaXN0CmRyaS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5v cmcKaHR0cHM6Ly9saXN0cy5mcmVlZGVza3RvcC5vcmcvbWFpbG1hbi9saXN0aW5mby9kcmktZGV2 ZWwK