From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout12.his.huawei.com (canpmsgout12.his.huawei.com [113.46.200.227]) (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 6A5E81F92E; Tue, 24 Feb 2026 01:30:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.227 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771896643; cv=none; b=Dtj6sc0bSrnEyYJ5o8sn0YdCQlSToCvtCzLJCMQLSrDAAu9msrcM8OsiwGKe5gFOvmf1ZsgwqpULaFcKGjYEJR+FlixwoZI4PzP4OfCf7FNU72GJKsy4P4hlXANqUbIVHRlo2Pl6w89TnNGxWGpNWgF1XwjSwuPSBlKbefpNk9g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771896643; c=relaxed/simple; bh=ZGpbjO+WU5On/I75If00vo6Wru1h2W4dyUxA+CMV3og=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=P4xla6erKy7NZbsg27Q03NQNsmnHGGoztykhMqQdICDB6OKp2bONe55qPkMejDDsw0XH6M4BjeOy0DJAM44OrDNjAZKxNMoTrtAgSBxa7I/9MKpa0RF70xqm+USKIgVZXUlGygIzl1klnwN+jDLZebtI7ID+CF2MmpjstOwiCRY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=FOwP6hge; arc=none smtp.client-ip=113.46.200.227 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="FOwP6hge" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=YxJR66oPaQm74nkXfQW8ipWh/0NdzqGNUh8ajE84pzs=; b=FOwP6hge41wJG6n0sf1CamOp0/PL7Nic/Vn/CJF3FgzfmmGQYgLTaPk56vsKG3m5BhyBWQXjv c3nmbOf1ksl8bV31nLV5mMFL+kCnaOUM++4Vdgh4Jb7rgVIyn8p5QpwqpK9bn1GypqZ9N9dNWBk 4v9XghGNub5hRIc89yCUh98= Received: from mail.maildlp.com (unknown [172.19.163.127]) by canpmsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4fKg5n72sMznTVV; Tue, 24 Feb 2026 09:25:49 +0800 (CST) Received: from kwepemk500005.china.huawei.com (unknown [7.202.194.90]) by mail.maildlp.com (Postfix) with ESMTPS id 72532402AB; Tue, 24 Feb 2026 09:30:31 +0800 (CST) Received: from [10.174.178.46] (10.174.178.46) by kwepemk500005.china.huawei.com (7.202.194.90) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 24 Feb 2026 09:30:30 +0800 Subject: Re: [PATCH] dcache: Limit the minimal number of bucket to two To: , CC: , , Jan Kara , Christoph Hellwig References: <20260130034853.215819-1-chengzhihao1@huawei.com> From: Zhihao Cheng Message-ID: Date: Tue, 24 Feb 2026 09:30:28 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20260130034853.215819-1-chengzhihao1@huawei.com> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To kwepemk500005.china.huawei.com (7.202.194.90) ÔÚ 2026/1/30 11:48, Zhihao Cheng дµÀ: friendly ping... > There is an OOB read problem on dentry_hashtable when user sets > 'dhash_entries=1': > BUG: unable to handle page fault for address: ffff888b30b774b0 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > Oops: Oops: 0000 [#1] SMP PTI > RIP: 0010:__d_lookup+0x56/0x120 > Call Trace: > d_lookup.cold+0x16/0x5d > lookup_dcache+0x27/0xf0 > lookup_one_qstr_excl+0x2a/0x180 > start_dirop+0x55/0xa0 > simple_start_creating+0x8d/0xa0 > debugfs_start_creating+0x8c/0x180 > debugfs_create_dir+0x1d/0x1c0 > pinctrl_init+0x6d/0x140 > do_one_initcall+0x6d/0x3d0 > kernel_init_freeable+0x39f/0x460 > kernel_init+0x2a/0x260 > > There will be only one bucket in dentry_hashtable when dhash_entries is > set as one, and d_hash_shift is calculated as 32 by dcache_init(). Then, > following process will access more than one buckets(which memory region > is not allocated) in dentry_hashtable: > d_lookup > b = d_hash(hash) > dentry_hashtable + ((u32)hashlen >> d_hash_shift) > // The C standard defines the behavior of right shift amounts > // exceeding the bit width of the operand as undefined. The > // result of '(u32)hashlen >> d_hash_shift' becomes 'hashlen', > // so 'b' will point to an unallocated memory region. > hlist_bl_for_each_entry_rcu(b) > hlist_bl_first_rcu(head) > h->first // read OOB! > > Fix it by limiting the minimal number of dentry_hashtable bucket to two, > so that 'd_hash_shift' won't exceeds the bit width of type u32. > > Cc: stable@vger.kernel.org > Signed-off-by: Zhihao Cheng > --- > fs/dcache.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index 66dd1bb830d1..957a44d2c44a 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -3260,7 +3260,7 @@ static void __init dcache_init_early(void) > HASH_EARLY | HASH_ZERO, > &d_hash_shift, > NULL, > - 0, > + 2, > 0); > d_hash_shift = 32 - d_hash_shift; > > @@ -3292,7 +3292,7 @@ static void __init dcache_init(void) > HASH_ZERO, > &d_hash_shift, > NULL, > - 0, > + 2, > 0); > d_hash_shift = 32 - d_hash_shift; > >