From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B48EEE7C4EB for ; Wed, 4 Oct 2023 18:14:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243995AbjJDSOD (ORCPT ); Wed, 4 Oct 2023 14:14:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243981AbjJDSOD (ORCPT ); Wed, 4 Oct 2023 14:14:03 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 810A5A7 for ; Wed, 4 Oct 2023 11:13:59 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA6F4C433CB; Wed, 4 Oct 2023 18:13:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1696443239; bh=XGYerxCja5vRRscmvujkaznUXZjL67D6/vtsmm/rFVk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=O8cdLKMi3JzgtJrDIHjy4U4h6vk3KTr6BZFQmA6t071T8IMdaf79dMHld2P12DuJc pTlTrb8dBYN56Cnseq6SLE029ibekhCW3AUw4p1UTrpQdcEdLhYqknvCsCIzt6nh9e ei5v43yCqgWAevq4l64GsNecXSULVfMoZJEsgSDo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ben Wolsieffer , Oleg Nesterov , Giulio Benetti , Greg Ungerer , Andrew Morton , Sasha Levin Subject: [PATCH 6.1 085/259] proc: nommu: /proc//maps: release mmap read lock Date: Wed, 4 Oct 2023 19:54:18 +0200 Message-ID: <20231004175221.265987714@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231004175217.404851126@linuxfoundation.org> References: <20231004175217.404851126@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ben Wolsieffer [ Upstream commit 578d7699e5c2add8c2e9549d9d75dfb56c460cb3 ] The no-MMU implementation of /proc//map doesn't normally release the mmap read lock, because it uses !IS_ERR_OR_NULL(_vml) to determine whether to release the lock. Since _vml is NULL when the end of the mappings is reached, the lock is not released. Reading /proc/1/maps twice doesn't cause a hang because it only takes the read lock, which can be taken multiple times and therefore doesn't show any problem if the lock isn't released. Instead, you need to perform some operation that attempts to take the write lock after reading /proc//maps. To actually reproduce the bug, compile the following code as 'proc_maps_bug': #include #include #include int main(int argc, char *argv[]) { void *buf; sleep(1); buf = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); puts("mmap returned"); return 0; } Then, run: ./proc_maps_bug &; cat /proc/$!/maps; fg Without this patch, mmap() will hang and the command will never complete. This code was incorrectly adapted from the MMU implementation, which at the time released the lock in m_next() before returning the last entry. The MMU implementation has diverged further from the no-MMU version since then, so this patch brings their locking and error handling into sync, fixing the bug and hopefully avoiding similar issues in the future. Link: https://lkml.kernel.org/r/20230914163019.4050530-2-ben.wolsieffer@hefring.com Fixes: 47fecca15c09 ("fs/proc/task_nommu.c: don't use priv->task->mm") Signed-off-by: Ben Wolsieffer Acked-by: Oleg Nesterov Cc: Giulio Benetti Cc: Greg Ungerer Cc: Signed-off-by: Andrew Morton Stable-dep-of: fe4419801617 ("proc: nommu: fix empty /proc//maps") Signed-off-by: Sasha Levin --- fs/proc/task_nommu.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index 2fd06f52b6a44..bfcf17f75ed50 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -205,11 +205,16 @@ static void *m_start(struct seq_file *m, loff_t *pos) return ERR_PTR(-ESRCH); mm = priv->mm; - if (!mm || !mmget_not_zero(mm)) + if (!mm || !mmget_not_zero(mm)) { + put_task_struct(priv->task); + priv->task = NULL; return NULL; + } if (mmap_read_lock_killable(mm)) { mmput(mm); + put_task_struct(priv->task); + priv->task = NULL; return ERR_PTR(-EINTR); } @@ -218,23 +223,21 @@ static void *m_start(struct seq_file *m, loff_t *pos) if (vma) return vma; - mmap_read_unlock(mm); - mmput(mm); return NULL; } -static void m_stop(struct seq_file *m, void *_vml) +static void m_stop(struct seq_file *m, void *v) { struct proc_maps_private *priv = m->private; + struct mm_struct *mm = priv->mm; - if (!IS_ERR_OR_NULL(_vml)) { - mmap_read_unlock(priv->mm); - mmput(priv->mm); - } - if (priv->task) { - put_task_struct(priv->task); - priv->task = NULL; - } + if (!priv->task) + return; + + mmap_read_unlock(mm); + mmput(mm); + put_task_struct(priv->task); + priv->task = NULL; } static void *m_next(struct seq_file *m, void *_p, loff_t *pos) -- 2.40.1