From patchwork Mon Aug 24 08:30:28 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 265192 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A6E1DC433DF for ; Mon, 24 Aug 2020 08:37:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 85B592177B for ; Mon, 24 Aug 2020 08:37:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598258253; bh=scT6Thky0JvXaho0x7iShlzBAYxDWBWqkWXwF7EqmPk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Bo9ofn5UyDs3jVQta3VQ2sVSQIxsWKdCmP+QpIFPy7TzV1T5Nl4D3MgtAgttkQKTm URu+8wboZaecfLZEK+kdX64UEk0c5ViKvz+9aWw8L60iFyqdA/yrSXzY1Nod+m/ZnI 6TET8oX6PYlWMmAPoxYcm9B1GRxWjXW5GB//DkwY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728422AbgHXIhb (ORCPT ); Mon, 24 Aug 2020 04:37:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:50912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728415AbgHXIha (ORCPT ); Mon, 24 Aug 2020 04:37:30 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0D57B2177B; Mon, 24 Aug 2020 08:37:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598258249; bh=scT6Thky0JvXaho0x7iShlzBAYxDWBWqkWXwF7EqmPk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cOJ0Dzro/e1tm8WiP9dFmsYzsfdVyg+PHbz5G7eDSwAG4Q4Im4b5LnX6WHmEq1xYy YVPaW5hm9xdQdEO42f4UDt4fjEB4kGRTgnVSYFTOocVdTKiFhl83S61ukzGs94+QI5 mulds9QhS37YR+OWUfvm0QpYwFDb93BAeveIKAL4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josef Bacik , Yonghong Song , Alexei Starovoitov , Sasha Levin Subject: [PATCH 5.8 130/148] bpf: Use get_file_rcu() instead of get_file() for task_file iterator Date: Mon, 24 Aug 2020 10:30:28 +0200 Message-Id: <20200824082420.243013589@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200824082413.900489417@linuxfoundation.org> References: <20200824082413.900489417@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Yonghong Song [ Upstream commit cf28f3bbfca097d956f9021cb710dfad56adcc62 ] With latest `bpftool prog` command, we observed the following kernel panic. BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor instruction fetch in kernel mode #PF: error_code(0x0010) - not-present page PGD dfe894067 P4D dfe894067 PUD deb663067 PMD 0 Oops: 0010 [#1] SMP CPU: 9 PID: 6023 ... RIP: 0010:0x0 Code: Bad RIP value. RSP: 0000:ffffc900002b8f18 EFLAGS: 00010286 RAX: ffff8883a405f400 RBX: ffff888e46a6bf00 RCX: 000000008020000c RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8883a405f400 RBP: ffff888e46a6bf50 R08: 0000000000000000 R09: ffffffff81129600 R10: ffff8883a405f300 R11: 0000160000000000 R12: 0000000000002710 R13: 000000e9494b690c R14: 0000000000000202 R15: 0000000000000009 FS: 00007fd9187fe700(0000) GS:ffff888e46a40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffffffffd6 CR3: 0000000de5d33002 CR4: 0000000000360ee0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: rcu_core+0x1a4/0x440 __do_softirq+0xd3/0x2c8 irq_exit+0x9d/0xa0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 RIP: 0033:0x47ce80 Code: Bad RIP value. RSP: 002b:00007fd9187fba40 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff13 RAX: 0000000000000002 RBX: 00007fd931789160 RCX: 000000000000010c RDX: 00007fd9308cdfb4 RSI: 00007fd9308cdfb4 RDI: 00007ffedd1ea0a8 RBP: 00007fd9187fbab0 R08: 000000000000000e R09: 000000000000002a R10: 0000000000480210 R11: 00007fd9187fc570 R12: 00007fd9316cc400 R13: 0000000000000118 R14: 00007fd9308cdfb4 R15: 00007fd9317a9380 After further analysis, the bug is triggered by Commit eaaacd23910f ("bpf: Add task and task/file iterator targets") which introduced task_file bpf iterator, which traverses all open file descriptors for all tasks in the current namespace. The latest `bpftool prog` calls a task_file bpf program to traverse all files in the system in order to associate processes with progs/maps, etc. When traversing files for a given task, rcu read_lock is taken to access all files in a file_struct. But it used get_file() to grab a file, which is not right. It is possible file->f_count is 0 and get_file() will unconditionally increase it. Later put_file() may cause all kind of issues with the above as one of sympotoms. The failure can be reproduced with the following steps in a few seconds: $ cat t.c #include #include #include #include #include #define N 10000 int fd[N]; int main() { int i; for (i = 0; i < N; i++) { fd[i] = open("./note.txt", 'r'); if (fd[i] < 0) { fprintf(stderr, "failed\n"); return -1; } } for (i = 0; i < N; i++) close(fd[i]); return 0; } $ gcc -O2 t.c $ cat run.sh #/bin/bash for i in {1..100} do while true; do ./a.out; done & done $ ./run.sh $ while true; do bpftool prog >& /dev/null; done This patch used get_file_rcu() which only grabs a file if the file->f_count is not zero. This is to ensure the file pointer is always valid. The above reproducer did not fail for more than 30 minutes. Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets") Suggested-by: Josef Bacik Signed-off-by: Yonghong Song Signed-off-by: Alexei Starovoitov Reviewed-by: Josef Bacik Link: https://lore.kernel.org/bpf/20200817174214.252601-1-yhs@fb.com Signed-off-by: Sasha Levin --- kernel/bpf/task_iter.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index ac7869a389990..a4a0fb4f94cc1 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -177,10 +177,11 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info, f = fcheck_files(curr_files, curr_fd); if (!f) continue; + if (!get_file_rcu(f)) + continue; /* set info->fd */ info->fd = curr_fd; - get_file(f); rcu_read_unlock(); return f; }