From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELvkvv1IOwO+0MS+fMrqRICM2QSgr7TK94QUOcJWMUm2kFf6AkrZSMKN/aV4z9RrzUX+iTL8 ARC-Seal: i=1; a=rsa-sha256; t=1520641324; cv=none; d=google.com; s=arc-20160816; b=uto2EJFYgdfzOJpBwe4mUvx/4WtAFNys7V21CjaUQb7zlfmGKDIkt7xwMZtP6bEfCf za2aBWCI1GPuNOsGRHxiSVZvBNugVK9GgOtapZcH1UYSoL0Z+zcQxuhSF9G0dRdXB0/a 6O2Jz5laZJqaIwgFZyQKof2Nyd8wEjT+GB4yf8d9mlbgEuSm8RlXzNtiZP3j856QoI70 zKxU8WTUUQjg8lyzJDox63cPDdYuc4w+TouSMBonfOsDmJf9MaNN0uyy5MNJpQT01G2W TYlucP6LxbTfA6upeb+lmCndblfTX9hzuh0D76QGNOX6YseqdSTcFT2ieRBh3CzPRW1x eQQA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=SGzH0W28TEH7Uc0dNkvzptp+25JvZJBtZift+pOWSAk=; b=AMQpJZbZuotNPKApvHYhiE5JCdsts9zQTaNc4eIkrTkGGat/a3/JqutxabbjwqyVSp zG9WJx8ZvIBIOB2K5Sr5koGD15feH35OmPW8yVCZiUy2wKWXgTOC270YwFE6rzWePFil VcYE4Qf2OOv3NSDaIMBAF2w8WenFKD+OWHQjeTc2kd8PhmxunFS4/LfptesyMEeF2Hor r/nZ0D7GTrs5UuamQENyJNONaUU/K2APAXq6jK8VthtA6azXMrGnHpV6p7lJz3acoIJ8 HF2l0qx5zQK4WNow92mjTz/qUj6gAuXVBrm4GefId4rAccNJWfkRS+35/Gd2Bne/93TQ yjkw== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 185.236.200.248 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 185.236.200.248 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Guillaume Nault , "David S. Miller" Subject: [PATCH 4.9 40/65] ppp: prevent unregistered channels from connecting to PPP units Date: Fri, 9 Mar 2018 16:18:40 -0800 Message-Id: <20180310001828.239056622@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180310001824.927996722@linuxfoundation.org> References: <20180310001824.927996722@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1594507820152251435?= X-GMAIL-MSGID: =?utf-8?q?1594507997291838429?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Guillaume Nault [ Upstream commit 77f840e3e5f09c6d7d727e85e6e08276dd813d11 ] PPP units don't hold any reference on the channels connected to it. It is the channel's responsibility to ensure that it disconnects from its unit before being destroyed. In practice, this is ensured by ppp_unregister_channel() disconnecting the channel from the unit before dropping a reference on the channel. However, it is possible for an unregistered channel to connect to a PPP unit: register a channel with ppp_register_net_channel(), attach a /dev/ppp file to it with ioctl(PPPIOCATTCHAN), unregister the channel with ppp_unregister_channel() and finally connect the /dev/ppp file to a PPP unit with ioctl(PPPIOCCONNECT). Once in this situation, the channel is only held by the /dev/ppp file, which can be released at anytime and free the channel without letting the parent PPP unit know. Then the ppp structure ends up with dangling pointers in its ->channels list. Prevent this scenario by forbidding unregistered channels from connecting to PPP units. This maintains the code logic by keeping ppp_unregister_channel() responsible from disconnecting the channel if necessary and avoids modification on the reference counting mechanism. This issue seems to predate git history (successfully reproduced on Linux 2.6.26 and earlier PPP commits are unrelated). Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- drivers/net/ppp/ppp_generic.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -3157,6 +3157,15 @@ ppp_connect_channel(struct channel *pch, goto outl; ppp_lock(ppp); + spin_lock_bh(&pch->downl); + if (!pch->chan) { + /* Don't connect unregistered channels */ + spin_unlock_bh(&pch->downl); + ppp_unlock(ppp); + ret = -ENOTCONN; + goto outl; + } + spin_unlock_bh(&pch->downl); if (pch->file.hdrlen > ppp->file.hdrlen) ppp->file.hdrlen = pch->file.hdrlen; hdrlen = pch->file.hdrlen + 2; /* for protocol bytes */