From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793093873; b=aeHOkC/Yfe64jx/ScyQz2PfyXpM248QI9grfdHytW89ZVDadGSwt4Jecsin3WfJbzFkK ENbhKvEJyfCnaenYHAapJ5ALB2iTYRnNk+srHd2IBkq/BR/40R782dmc/qIHEKz8XVSl3 JZyyK48sVLoX29oLhXVY6ixipjQEToLNf7OCoTRdj+q1L/r16/3oYYcvGXsWqIPQSHSYt 1zdz4UHGm9cfkanQSYmXNDKPcNKo6loJJnAnTdLW0Keg6vuE3Bu+9xOiF/XIZp1WwblS6 QVstsT2vlwH0MhKnNiGrTKMFphVgK2wcax96gjWhhjAY9BZlKLaDBMqSy+3jcU/IhEA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793093873; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=+rNSdhvOTHmuEN3Ml/bfsrTqF8UwvJdcqDi4DNQ6sTg=; b=BNoowM04eRTfOb4kDWjStN1Nj+6UGSUi+P6MjFiL0K9185ewYg+VJIXR0tSg0mEgPXnH vKVkKXMOkgCHkP+T5v2zoHstMUm2BLVakzktGRDpg9vZlAn0frXbv9UkIIWlV/B14ttwz wDsUXca9zHJ4Rwc36S4ci2FEhwVVYj4iXvgzcVkGBAaF+fY66SIipZHQI3gsJ4h0j8y/4 GloN0f3T1gMCtwTB629hgrrTOFuBSyP7wV1erZZKHynXza5TUr+yWtMQdgDS9JuzaVRjb 0jqDia9C6mmHjqpAYdtdOky+Y/JDw+l87lQuc27vOXS7Xp0ZRNXn6kppVwqItRDKjAQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=U7+fBT3l; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B781F606A31A; Tue, 27 Oct 2026 09:37:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=U7+fBT3l Received: by smtp.kernel.org (Postfix) with ESMTPSA id 490C11F01825; Tue, 27 Oct 2026 09:37:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793093872; bh=+rNSdhvOTHmuEN3Ml/bfsrTqF8UwvJdcqDi4DNQ6sTg=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=U7+fBT3lehpQpFc3uJKZHtVpRgi1GtGHT6z3b8kE2S6FeF6bFDBDYsG/DhyOz1wlU gkZvgV/b8GwC5hBF2vuMNqTpih+mBOGm/magVJ+5tlmYMUc8rC0HgDbxkq4C2ZdX7/ ykFSl8AC+Hlev3LyWJ5Ey8IgtYvUDz6NSxnqxhKKoOE4gmRJYKRD4ktRxpkFHa/N0B GZx6g/C9Es4dpnIsGGa84PHZ4w1B6j/LHsH9niHHf9ry4zHK8ev9PN5ziVl0zIXEG7 p4yl/pvZrQHfp2KrQDErkAMPWJNescqIgRyziMHz4MrRviwMpP912C23Dpz/85S7eu i5GpXe5pXwalg== Date: Tue, 27 Oct 2026 09:37:34 +0000 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH 21/46] mm/gup: fix out-of-bounds write for nr_pages == 0 in GUP-fast Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-21-6f74bec9a5bb@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-21-6f74bec9a5bb@kernel.org> On Tue, Oct 27, 2026 at 12:17:41AM +0100, David Hildenbrand (Arm) wrote: > From: Chris Mason > > With nr_pages == 0, GUP-fast still enters its page table walk and can > write past the caller's page array. The old end <= start check caught > empty ranges, but was replaced with an overflow check. > > Users such as OrangeFS can pass a zero page count derived from a > userspace-supplied length. So let's return zero for nr_pages == 0 before > starting the walk, just like GUP-slow. > > Fix generated by an LLM and sent by Chris Mason in private. > > Fixes: c28b1fc70390 ("mm/gup: reorganize internal_get_user_pages_fast()") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Mason > [ david: simplify description ] > Signed-off-by: David Hildenbrand (Arm) LGTM so: Reviewed-by: Lorenzo Stoakes (ARM) > --- > mm/gup.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 47e7ae152cdf1..9906965893431 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -3204,6 +3204,9 @@ static int gup_fast_fallback(unsigned long start, unsigned long nr_pages, > FOLL_PCI_P2PDMA | FOLL_HONOR_NUMA_FAULT))) > return -EINVAL; > > + if (unlikely(!nr_pages)) > + return 0; > + > if (gup_flags & FOLL_PIN) > mm_set_has_pinned_flag(current->mm); > > > -- > 2.43.0 > -- Cheers, Lorenzo