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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 6706CE9D3FA for ; Wed, 4 Feb 2026 15:07:20 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9A1A810E6AF; Wed, 4 Feb 2026 15:07:19 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id 5E5DA10E689 for ; Wed, 4 Feb 2026 15:07:18 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7962B150C for ; Wed, 4 Feb 2026 07:07:11 -0800 (PST) Received: from [192.168.0.1] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A263E3F778 for ; Wed, 4 Feb 2026 07:07:17 -0800 (PST) Date: Wed, 4 Feb 2026 15:05:39 +0000 From: Liviu Dudau To: Alexander Konyukhov Cc: Brian Starkey , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , "dri-devel@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" , "lvc-project@linuxtesting.org" , "nd@arm.com" Subject: Re: [PATCH] drm/komeda: fix integer overflow in AFBC framebuffer size check Message-ID: References: <20260203134907.1587067-1-Alexander.Konyukhov@kaspersky.com> <57df230af1624c679a947317152fd8ed@kaspersky.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <57df230af1624c679a947317152fd8ed@kaspersky.com> 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: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, Feb 04, 2026 at 02:56:38PM +0000, Alexander Konyukhov wrote: > Thank you for the replies. > > According to ISO 9899 6.3.1 both operands are first converted to a common type (u32), there are no defined limits of kfb->afbc_size and fb->offsets[0] , so min_size can have an overflowed u32 value. Yes, but according to the komeda_framebuffer.c file, line 48, the min_size is an u64 variable, so it can hold the result of adding two u32 values safely. Best regards, Liviu > > -----Original Message----- > From: Liviu Dudau > Sent: Wednesday, February 4, 2026 4:25 PM > To: Brian Starkey > Cc: Alexander Konyukhov ; Maarten Lankhorst ; Maxime Ripard ; Thomas Zimmermann ; David Airlie ; Simona Vetter ; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; lvc-project@linuxtesting.org; nd@arm.com > Subject: Re: [PATCH] drm/komeda: fix integer overflow in AFBC framebuffer size check > > Caution: This is an external email. > > > > On Tue, Feb 03, 2026 at 09:43:12PM +0000, Brian Starkey wrote: > > Hi Alexander, > > > > On Tue, Feb 03, 2026 at 04:48:46PM +0000, Alexander Konyukhov wrote: > > > The AFBC framebuffer size validation calculates the minimum required > > > buffer size by adding the AFBC payload size to the framebuffer offset. > > > This addition is performed without checking for integer overflow. > > > > > > If the addition oveflows, the size check may incorrectly succed and > > > allow userspace to provide an undersized drm_gem_object, potentially > > > leading to out-of-bounds memory access. > > > > > > Add usage of check_add_overflow() to safely compute the minimum > > > required size and reject the framebuffer if an overflow is detected. > > > This makes the AFBC size validation more robust against malformed. > > > > > > Found by Linux Verification Center (linuxtesting.org) with SVACE. > > > > > > Fixes: 65ad2392dd6d ("drm/komeda: Added AFBC support for komeda > > > driver") > > > Signed-off-by: Alexander Konyukhov > > > > > > --- > > > drivers/gpu/drm/arm/display/komeda/komeda_framebuffer.c | 6 +++++- > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_framebuffer.c > > > b/drivers/gpu/drm/arm/display/komeda/komeda_framebuffer.c > > > index 3ca461eb0a24..3cb34d03f7f8 100644 > > > --- a/drivers/gpu/drm/arm/display/komeda/komeda_framebuffer.c > > > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_framebuffer.c > > > @@ -4,6 +4,8 @@ > > > * Author: James.Qian.Wang > > > * > > > */ > > > +#include > > > + > > > #include > > > #include > > > #include > > > @@ -93,7 +95,9 @@ komeda_fb_afbc_size_check(struct komeda_fb *kfb, struct drm_file *file, > > > kfb->afbc_size = kfb->offset_payload + n_blocks * > > > ALIGN(bpp * AFBC_SUPERBLK_PIXELS / 8, > > > AFBC_SUPERBLK_ALIGNMENT); > > > - min_size = kfb->afbc_size + fb->offsets[0]; > > > > Can this really overflow? Is the concern a hypothetical ILP64 > > situation? > > > > min_size is u64, kfb->afbc_size is u32, and fb->offsets[0] is unsigned > > int. > > Yeah, I was thinking the same thing yesterday at the end of the work day when I looked at the patch. I don't think following the call flow you can end up with an overflow. > > Best regards, > Liviu > > > > > Thanks, > > -Brian > > > > > + if (check_add_overflow(kfb->afbc_size, fb->offsets[0], &min_size)) { > > > + goto check_failed; > > > + } > > > if (min_size > obj->size) { > > > DRM_DEBUG_KMS("afbc size check failed, obj_size: 0x%zx. min_size 0x%llx.\n", > > > obj->size, min_size); > > > -- > > > 2.43.0 > > >