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 2F55AEB64DC for ; Mon, 3 Jul 2023 16:18:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230242AbjGCQS2 (ORCPT ); Mon, 3 Jul 2023 12:18:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49132 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229932AbjGCQS2 (ORCPT ); Mon, 3 Jul 2023 12:18:28 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27AC6138; Mon, 3 Jul 2023 09:18:27 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id AA12160F53; Mon, 3 Jul 2023 16:18:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D59DC433C7; Mon, 3 Jul 2023 16:18:25 +0000 (UTC) Date: Mon, 3 Jul 2023 12:18:23 -0400 From: Steven Rostedt To: Mateusz Stachyra Cc: "linux-kernel@vger.kernel.org" , "linux-trace-kernel@vger.kernel.org" , "mhiramat@kernel.org" Subject: Re: [PATCH] trace: fix null pointer dereference in tracing_err_log_open() Message-ID: <20230703121823.5d96c1cb@gandalf.local.home> In-Reply-To: <20230703155237eucms1p4dfb6a19caa14c79eb6c823d127b39024@eucms1p4> References: <20230703155237eucms1p4dfb6a19caa14c79eb6c823d127b39024@eucms1p4> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org On Mon, 03 Jul 2023 17:52:37 +0200 Mateusz Stachyra wrote: > >From d6ef949d29b884dd77fe5e628dc71318de08868c Mon Sep 17 00:00:00 2001 > From: Mateusz Stachyra > Date: Mon, 3 Jul 2023 17:48:40 +0200 > Subject: [PATCH] trace: fix null pointer dereference in tracing_err_log_open() > > Fix an issue in function 'tracing_err_log_open'. > The function doesn't call 'seq_open' if file is opened only with > write permissions, which results in 'file->private_data' being left at null. > If we then use 'lseek' on that opened file, 'seq_lseek' dereferences > 'file->private_data' in 'mutex_lock(&m->lock)', resulting in a Kernel panic. > Writing to this node requires root privilages, therefore this bug > has very little security impact. > > Tracefs node: /sys/kernel/tracing/error_log > Nice catch, but I recommend a different solution. > Example Kernel panic: > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038 > Call trace: > mutex_lock+0x30/0x110 > seq_lseek+0x34/0xb8 > __arm64_sys_lseek+0x6c/0xb8 > invoke_syscall+0x58/0x13c > el0_svc_common+0xc4/0x10c > do_el0_svc+0x24/0x98 > el0_svc+0x24/0x88 > el0t_64_sync_handler+0x84/0xe4 > el0t_64_sync+0x1b4/0x1b8 > Code: d503201f aa0803e0 aa1f03e1 aa0103e9 (c8e97d02) > ---[ end trace 561d1b49c12cf8a5 ]--- > Kernel panic - not syncing: Oops: Fatal exception > > Signed-off-by: Mateusz Stachyra > --- > kernel/trace/trace.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 5d2c5678b..bfa8e2d01 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -8097,8 +8097,16 @@ static int tracing_err_log_open(struct inode *inode, struct file *file) > return ret; > > /* If this file was opened for write, then erase contents */ > - if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) > + if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) { > clear_tracing_err_log(tr); > + ret = seq_open(file, &tracing_err_log_seq_ops); > + if (!ret) { > + struct seq_file *m = file->private_data; > + m->private = tr; > + } else { > + trace_array_put(tr); > + } > + } > > if (file->f_mode & FMODE_READ) { > ret = seq_open(file, &tracing_err_log_seq_ops); > > base-commit: 1ef6663a587ba3e57dc5065a477db1c64481eedd I believe this can be better fixed by: diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 64a4dde073ef..999b7c73e324 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8135,7 +8135,7 @@ static const struct file_operations tracing_err_log_fops = { .open = tracing_err_log_open, .write = tracing_err_log_write, .read = seq_read, - .llseek = seq_lseek, + .llseek = tracing_lseek, .release = tracing_err_log_release, }; as that tracing_lseek() is for this exact scenario. Care to send a v2? Thanks, -- Steve