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Thu, 18 Jan 2024 02:43:04 +0000 (UTC) X-FDA: 81690884688.22.46AEC1A Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) by imf24.hostedemail.com (Postfix) with ESMTP id 3066D180006 for ; Thu, 18 Jan 2024 02:43:00 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=none; spf=pass (imf24.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.113 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1705545782; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tRU9E5+d50z0ZVwCm0RGnw3XPFcA15P55QcgWKlK2nE=; b=OHflucdaydNDhrKOi2Bv2Z8RE+pu6PXBX2I7uJhMdv6Q1z9ZVdyeWVgOUoPSmYgNC9cKkc 7iuMVIwUceei/szcdgU+kUf4rwBk4yk6WtEZveuWEBdZuB7v8U0uzHZdJ3RVo4l0lxnUQG kT1fN0kZ8sgLwc7TW4Znq0RO3vVmSVg= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1705545782; a=rsa-sha256; cv=none; b=yuHCxqDKo3+xO6QCSRtL7SumC2jpnBSGqW3GhCd2OuFfGfpyw9Ov+MjyUUIXMHp0MfxAxx 34vUzJEGpDlb5DkV+K/e02zN2GBN52XPO+NJUpaGwcZxF4fxlefHmn29tBX5JYl/KKWcQx HUgs+a+jlxt2lmDPR5Ovtojjc7CEOFM= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none; spf=pass (imf24.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.113 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045176;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0W-r3A6E_1705545775; Received: from 30.97.48.47(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W-r3A6E_1705545775) by smtp.aliyun-inc.com; Thu, 18 Jan 2024 10:42:56 +0800 Message-ID: Date: Thu, 18 Jan 2024 10:43:26 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs: improve dump_mapping() robustness To: Al Viro Cc: akpm@linux-foundation.org, willy@infradead.org, brauner@kernel.org, jack@suse.cz, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <937ab1f87328516821d39be672b6bc18861d9d3e.1705391420.git.baolin.wang@linux.alibaba.com> <20240118013857.GO1674809@ZenIV> From: Baolin Wang In-Reply-To: <20240118013857.GO1674809@ZenIV> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 3066D180006 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 5opoacw87bqohwspnixgeppyjmt7sw34 X-HE-Tag: 1705545780-280979 X-HE-Meta: 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 AGM+vGkQ xdBF8hzfukq3qd/Q2b0XzNUDDkHvFVUT0I7y1rZV+j1ojnVIuCAk431kVlL7DIpCrGJA+GORcQVIJSg0Od06I76MYFUtKriZORUvH+6jNxbnQt+zIwBCiXO2sqUznRiG0B/lYSDfshj8fIwlyGGESFRj4Ie9JBnfjZA19+I4lqPMVN2qD42ZGqNMOlT0yifSUAr3w9F9Y9SIKVlQ+4/A8QFheoXgaoEpOcA0T X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/18/2024 9:38 AM, Al Viro wrote: > On Tue, Jan 16, 2024 at 03:53:35PM +0800, Baolin Wang wrote: > >> With checking the 'dentry.parent' and 'dentry.d_name.name' used by >> dentry_name(), I can see dump_mapping() will output the invalid dentry >> instead of crashing the system when this issue is reproduced again. > >> dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias); >> - if (get_kernel_nofault(dentry, dentry_ptr)) { >> + if (get_kernel_nofault(dentry, dentry_ptr) || >> + !dentry.d_parent || !dentry.d_name.name) { >> pr_warn("aops:%ps ino:%lx invalid dentry:%px\n", >> a_ops, ino, dentry_ptr); >> return; > > That's nowhere near enough. Your ->d_name.name can bloody well be pointing > to an external name that gets freed right under you. Legitimately so. > > Think what happens if dentry has a long name (longer than would fit into > the embedded array) and gets renamed name just after you copy it into > a local variable. Old name will get freed. Yes, freeing is RCU-delayed, > but I don't see anything that would prevent your thread losing CPU > and not getting it back until after the sucker's been freed. Yes, that's possible. And this appears to be a use-after-free issue in the existing code, which is different from the issue that my patch addressed. So how about adding a rcu_read_lock() before copying the dentry to a local variable in case the old name is freed?