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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 595FCC3F2D3 for ; Fri, 28 Feb 2020 11:54:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3BA12246B0 for ; Fri, 28 Feb 2020 11:54:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726687AbgB1LyK (ORCPT ); Fri, 28 Feb 2020 06:54:10 -0500 Received: from mx2.suse.de ([195.135.220.15]:34714 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725884AbgB1LyJ (ORCPT ); Fri, 28 Feb 2020 06:54:09 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 9A9B3B3A2; Fri, 28 Feb 2020 11:54:07 +0000 (UTC) From: Jiri Slaby To: gregkh@linuxfoundation.org Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Jiri Slaby , syzbot+26183d9746e62da329b8@syzkaller.appspotmail.com Subject: [PATCH 2/2] vt: selection, push sel_lock up Date: Fri, 28 Feb 2020 12:54:06 +0100 Message-Id: <20200228115406.5735-2-jslaby@suse.cz> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200228115406.5735-1-jslaby@suse.cz> References: <20200228115406.5735-1-jslaby@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org sel_lock cannot nest in the console lock. Thanks to syzkaller, the kernel states firmly: > WARNING: possible circular locking dependency detected > 5.6.0-rc3-syzkaller #0 Not tainted > ------------------------------------------------------ > syz-executor.4/20336 is trying to acquire lock: > ffff8880a2e952a0 (&tty->termios_rwsem){++++}, at: tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 > > but task is already holding lock: > ffffffff89462e70 (sel_lock){+.+.}, at: paste_selection+0x118/0x470 drivers/tty/vt/selection.c:374 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #2 (sel_lock){+.+.}: > mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118 > set_selection_kernel+0x3b8/0x18a0 drivers/tty/vt/selection.c:217 > set_selection_user+0x63/0x80 drivers/tty/vt/selection.c:181 > tioclinux+0x103/0x530 drivers/tty/vt/vt.c:3050 > vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 This is ioctl(TIOCL_SETSEL). Locks held on the path: console_lock -> sel_lock > -> #1 (console_lock){+.+.}: > console_lock+0x46/0x70 kernel/printk/printk.c:2289 > con_flush_chars+0x50/0x650 drivers/tty/vt/vt.c:3223 > n_tty_write+0xeae/0x1200 drivers/tty/n_tty.c:2350 > do_tty_write drivers/tty/tty_io.c:962 [inline] > tty_write+0x5a1/0x950 drivers/tty/tty_io.c:1046 This is write(). Locks held on the path: termios_rwsem -> console_lock > -> #0 (&tty->termios_rwsem){++++}: > down_write+0x57/0x140 kernel/locking/rwsem.c:1534 > tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 > mkiss_receive_buf+0x12aa/0x1340 drivers/net/hamradio/mkiss.c:902 > tty_ldisc_receive_buf+0x12f/0x170 drivers/tty/tty_buffer.c:465 > paste_selection+0x346/0x470 drivers/tty/vt/selection.c:389 > tioclinux+0x121/0x530 drivers/tty/vt/vt.c:3055 > vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 This is ioctl(TIOCL_PASTESEL). Locks held on the path: sel_lock -> termios_rwsem > other info that might help us debug this: > > Chain exists of: > &tty->termios_rwsem --> console_lock --> sel_lock Clearly. From the above, we have: console_lock -> sel_lock sel_lock -> termios_rwsem termios_rwsem -> console_lock Fix this by reversing the console_lock -> sel_lock dependency in ioctl(TIOCL_SETSEL). First, lock sel_lock, then console_lock. Signed-off-by: Jiri Slaby Reported-by: syzbot+26183d9746e62da329b8@syzkaller.appspotmail.com Fixes: 07e6124a1a46 ("vt: selection, close sel_buffer race") --- drivers/tty/vt/selection.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) diff --git a/drivers/tty/vt/selection.c b/drivers/tty/vt/selection.c index 5b0b897396eb..7556139cd0da 100644 --- a/drivers/tty/vt/selection.c +++ b/drivers/tty/vt/selection.c @@ -219,7 +219,6 @@ static int __set_selection_kernel(struct tiocl_selection *v, struct tty_struct * if (ps > pe) /* make sel_start <= sel_end */ swap(ps, pe); - mutex_lock(&sel_lock); if (sel_cons != vc_cons[fg_console].d) { clear_selection(); sel_cons = vc_cons[fg_console].d; @@ -265,10 +264,9 @@ static int __set_selection_kernel(struct tiocl_selection *v, struct tty_struct * break; case TIOCL_SELPOINTER: highlight_pointer(pe); - goto unlock; + return 0; default: - ret = -EINVAL; - goto unlock; + return -EINVAL; } /* remove the pointer */ @@ -290,7 +288,7 @@ static int __set_selection_kernel(struct tiocl_selection *v, struct tty_struct * else if (new_sel_start == sel_start) { if (new_sel_end == sel_end) /* no action required */ - goto unlock; + return 0; else if (new_sel_end > sel_end) /* extend to right */ highlight(sel_end + 2, new_sel_end); else /* contract from right */ @@ -318,8 +316,7 @@ static int __set_selection_kernel(struct tiocl_selection *v, struct tty_struct * if (!bp) { printk(KERN_WARNING "selection: kmalloc() failed\n"); clear_selection(); - ret = -ENOMEM; - goto unlock; + return -ENOMEM; } kfree(sel_buffer); sel_buffer = bp; @@ -344,8 +341,7 @@ static int __set_selection_kernel(struct tiocl_selection *v, struct tty_struct * } } sel_buffer_lth = bp - sel_buffer; -unlock: - mutex_unlock(&sel_lock); + return ret; } @@ -353,9 +349,11 @@ int set_selection_kernel(struct tiocl_selection *v, struct tty_struct *tty) { int ret; + mutex_lock(&sel_lock); console_lock(); ret = __set_selection_kernel(v, tty); console_unlock(); + mutex_unlock(&sel_lock); return ret; } -- 2.25.1