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 0F80F3A1DB; Sun, 11 Jan 2026 11:32:21 +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=1768131142; cv=none; b=FqBYryUK+e2acX+CUtMt/IDWM44V/b2vJBxDL3Xxr7dJcpjCXimDCzBuixzHaZvz/bAW1cqvvfWoEJDr6XdlMZjRDKpBg0A4L6wgkPRhR1yUvb81QHO2qGW49xnVdInZ3DxRcLmvNyQcqRQUareTk2nrGhZxyUq3M+TdEUBkiFg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768131142; c=relaxed/simple; bh=7ouPXljRdS3wEh7LWykxzjsCuZAvXUsWhsf54tJGDaY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=l/wnAoDii3gi611/5YhXZmpsnGwP99LEWCS4Kp/36/VuWgd9MVxzn3p7K017+g9pXIDfDiXaQbBYKDVPx/C6NKWkvtp9730VSAgJOcVIwZ/7tlrmA0Q2DwibAunAOXB3XLy5aoFfaWmpuKM6tY9SG5k1fUqFFsMWLn3+JR8a4Wc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pXlziS46; 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="pXlziS46" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1169CC4CEF7; Sun, 11 Jan 2026 11:32:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768131141; bh=7ouPXljRdS3wEh7LWykxzjsCuZAvXUsWhsf54tJGDaY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=pXlziS46JbQtb4obUeCUECjyqyJEr5ZyH9nT5h4jLiAn/widU8KKyug6r0Wl1Ti+W PiGyBqzBXkSvyvo3laN4Pl4cBsaQOg8P+a8T6Oxr9VziYksODwviTnIPhLaadPQ/H6 sF0+N5pbr0PuiJ0TAN5xD8THer42SZvOSRYv6heBjoE0sF/Cy1F+/cZr10v/RTiDlk NUNqU6fCZmfY7WoW1uq/8U5HPTI9v0KMPNgsMZvA9Csqg/D33YK1fyNmzB8A1QQa+P z6b2WH1VkuF8OrL1v12ThaON4SRFgn0yYPvAUI6J1hcZBJg11Mfk/Lri7szuR8klly of9GEpYkhJZUg== Message-ID: <95f3dae0-fc8c-43a8-aa37-8393e66cc75b@kernel.org> Date: Sun, 11 Jan 2026 12:32:13 +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; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAa2VybmVsLm9yZz7CwY0EEwEIADcWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaKYhwAIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA/4Naa5EP/3a1 9sgS9m7oiR0uenlj+C6kkIKlpWKRfGH/WvtFaHr/y06TKnWn6cMOZzJQ+8S39GOteyCCGADh 6ceBx1KPf6/AvMktnGETDTqZ0N9roR4/aEPSMt8kHu/GKR3gtPwzfosX2NgqXNmA7ErU4puf zica1DAmTvx44LOYjvBV24JQG99bZ5Bm2gTDjGXV15/X159CpS6Tc2e3KvYfnfRvezD+alhF XIym8OvvGMeo97BCHpX88pHVIfBg2g2JogR6f0PAJtHGYz6M/9YMxyUShJfo0Df1SOMAbU1Q Op0Ij4PlFCC64rovjH38ly0xfRZH37DZs6kP0jOj4QdExdaXcTILKJFIB3wWXWsqLbtJVgjR YhOrPokd6mDA3gAque7481KkpKM4JraOEELg8pF6eRb3KcAwPRekvf/nYVIbOVyT9lXD5mJn IZUY0LwZsFN0YhGhQJ8xronZy0A59faGBMuVnVb3oy2S0fO1y/r53IeUDTF1wCYF+fM5zo14 5L8mE1GsDJ7FNLj5eSDu/qdZIKqzfY0/l0SAUAAt5yYYejKuii4kfTyLDF/j4LyYZD1QzxLC MjQl36IEcmDTMznLf0/JvCHlxTYZsF0OjWWj1ATRMk41/Q+PX07XQlRCRcE13a8neEz3F6we 08oWh2DnC4AXKbP+kuD9ZP6+5+x1H1zEzsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCgh Cj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseB fDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts 6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiu Qmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKB Tccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvF FFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh 2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRk F3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0L LH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4v q7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmic2qsF CSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvVQ0x8xXvoGJwZ rk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q/y06TrTb1n4n 7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPFQKzhRRktBMK4 GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLoPn9kgHD3hRBa Yakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX63T6oO2Libzz 7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt2slI4VcPNnz+ vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMBgoisDB8ceYxO cFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY2x3snF8q7U9G EIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqBgzK8ePtDTqRM qZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8fa0= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/10/26 00:43, Andrii Nakryiko wrote: > On Tue, Jan 6, 2026 at 11:16 AM David Hildenbrand (Red Hat) > wrote: >> >> 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). >> > > That would be great. But something like this was proposed earlier and > Matthew didn't particularly like this approach ([0]). > > [0] https://lore.kernel.org/all/aReUv1kVACh3UKv-@casper.infradead.org/ Well, but on the higher level we don't know whether we have to even call into read_cache_folio(). Again, hugetlb. Might be worth reproducing with hugetlb/shmem, and making sure it keeps working even with your changes. -- Cheers David