From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CAD211C3BF7; Tue, 6 Jan 2026 19:16:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767727007; cv=none; b=bgxC/gKgGIFJsgTViuKteHMaur2l+Ie2exDBfAOJLZNNL9OqgpvbeS7hq/ureTHgQgoPPHiN/0J+k/IJE1D820f8S2rHfSpEq8P5WZE0IuQqXZNe0qr1kAWXh8KYoUJgXEnBWjS1Hjexd4uSOS3ptzB4BhEYxOCOF9WFDMj0eN8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767727007; c=relaxed/simple; bh=kop1kdncQM6zLNIQ0Pi3tZ1S0cklW8UyrfrrCgGMmIM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=a91D2aukk51TyfEwDv1tY8BkkdV3LapSAZm8C7iUcJxOWLfcI9icczQ3/Ckv0V7DxURDG4KuqS5+4NU4Bs95x0U2pyX1wN52suEIME7bfgGhfmptSayHSMZ4p/UjJBstKcZKlEkTyqWurNys1eErxVeIrbrJTxO6OxVwMfyKoa0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dVDyWgU3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dVDyWgU3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C0FAC116C6; Tue, 6 Jan 2026 19:16:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767727007; bh=kop1kdncQM6zLNIQ0Pi3tZ1S0cklW8UyrfrrCgGMmIM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=dVDyWgU3UhiNNMTMBv5fPHeNrNQOTdwvkVE32cAfKrhEWjSpEPbqawbKlbmbpydrt PYYql63acHS+cLJ2B2d6krXP4TRywbrcjRV8/aV4TaS64w1nO8HN69SLO41YxHsVZg zwshyk8G6U2AjiPuE9y2Yc4AiIR/ZlpXX0XKG+TKKwScc2bnoq1i/73//sR9TSuxn0 Q4cr9sPxcLoWVnjuzq9eDv2WvPehKb9Mou8dat4qEST/v6t/e4f77ZNhTSpk9Ng96J iCL8XFvWtonKH70HV5djoAOz7FyS2ezChQ6YFqqWHgBICm6cPU2Gx+aOMCxK4Iin+V mz39fUuHRSCww== Message-ID: Date: Tue, 6 Jan 2026 20:16:38 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] buildid: validate page-backed file before parsing build ID To: Andrii Nakryiko Cc: Andrew Morton , Jinchao Wang , Song Liu , Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, syzbot+e008db2ac01e282550ee@syzkaller.appspotmail.com, Axel Rasmussen , Johannes Weiner , Lorenzo Stoakes , Michal Hocko , Qi Zheng , Shakeel Butt , Wei Xu , Yuanchu Xie , Omar Sandoval , Deepanshu Kartikey References: <20251223103214.2412446-1-wangjinchao600@gmail.com> <20251223092932.0a804e046fc2e5de236ced69@linux-foundation.org> <86b3f8af-299a-4ae7-b2dc-0b068046fe92@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/5/26 23:52, Andrii Nakryiko wrote: > On Tue, Dec 30, 2025 at 2:11 PM David Hildenbrand (Red Hat) > wrote: >> >> On 12/23/25 18:29, Andrew Morton wrote: >>> On Tue, 23 Dec 2025 18:32:07 +0800 Jinchao Wang wrote: >>> >>>> __build_id_parse() only works on page-backed storage. Its helper paths >>>> eventually call mapping->a_ops->read_folio(), so explicitly reject VMAs >>>> that do not map a regular file or lack valid address_space operations. >>>> >>>> Reported-by: syzbot+e008db2ac01e282550ee@syzkaller.appspotmail.com >>>> Signed-off-by: Jinchao Wang >>>> >>>> ... >>>> >>>> --- a/lib/buildid.c >>>> +++ b/lib/buildid.c >>>> @@ -280,7 +280,10 @@ static int __build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, >>>> int ret; >>>> >>>> /* only works for page backed storage */ >>>> - if (!vma->vm_file) >>>> + if (!vma->vm_file || >>>> + !S_ISREG(file_inode(vma->vm_file)->i_mode) || >>>> + !vma->vm_file->f_mapping->a_ops || >>>> + !vma->vm_file->f_mapping->a_ops->read_folio) >>>> return -EINVAL; >> >> Just wondering, we are fine with MAP_PRIVATE files, right? I guess it's >> not about the actual content in the VMA (which might be different for a >> MAP_PRIVATE VMA), but only about the content of the mapped file. > > Yep, this code is fetching contents of a file that backs given VMA. Good! > >> >> >> LGTM, although I wonder whether some of these these checks should be >> exposed as part of the read_cache_folio()/do_read_cache_folio() API. >> >> Like, having a helper function that tells us whether we can use >> do_read_cache_folio() against a given mapping+file. > > I agree, this seems to be leaking a lot of internal mm details into > higher-level caller (__build_id_parse). Right now we try to fetch > folio with filemap_get_folio() and if that succeeds, then we do > read_cache_folio. Would it be possible for filemap_get_folio() to > return error if the folio cannot be read using read_cache_folio()? Or > maybe have a variant of filemap_get_folio() that would have this > semantic? Good question. But really, for files that always have everything in the pagecache, there would not be a problem, right? I'm thinking about hugetlb, for example. There, we never expect to fallback to do_read_cache_folio(). So maybe we could just teach do_read_cache_folio() to fail properly? diff --git a/mm/filemap.c b/mm/filemap.c index ebd75684cb0a7..3f81b8481af4c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -4051,8 +4051,11 @@ static struct folio *do_read_cache_folio(struct address_space *mapping, struct folio *folio; int err; - if (!filler) + if (!filler) { + if (!mapping->a_ops || !mapping->a_ops->read_folio) + return ERR_PTR(-EINVAL); filler = mapping->a_ops->read_folio; + } repeat: folio = filemap_get_folio(mapping, index); if (IS_ERR(folio)) { Then __build_id_parse() would only check for the existence of vma->vm_file and maybe the !S_ISREG(file_inode(vma->vm_file)->i_mode). -- Cheers David