From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from metis.whiteo.stw.pengutronix.de (metis.whiteo.stw.pengutronix.de [185.203.201.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B56381DAC95 for ; Wed, 6 Nov 2024 09:43:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.203.201.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730886193; cv=none; b=L4Ezw9zA1ACHbKQaRjOs5Wzzq1OUDAKS6RU+uCDb6kIaUjufI2/rL55siPb9+h+DohQTT2jUduuc6ReYLa5HST1eGhUPosBO7znzteqhDJqFhoq7TyEpq0vIdTwxoKbP0FEum6sTgeLkxUiMIGcl40yIsf0V9OaBJFuPjthESYQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730886193; c=relaxed/simple; bh=o5WzC5wKDT7nrFSU25/Vr4sHvTQ+DRwdgVhghX0UrCw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=l8MvilNxigbuZcSmHaGUUueCv3p8BfBf6Rzybqyw3jkTCLIZ1Gr0wJq5cktLCqChZfqBfIcgYah9/21F2Y1YVyFRNi2vKsOJ0+WHwO9Hhss4GyIL5msNWC2IIT/eoVCTXTbdztozhneCMTNKPI2jwsy05OX2EpidSNs6DlWYW3o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de; spf=pass smtp.mailfrom=pengutronix.de; arc=none smtp.client-ip=185.203.201.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pengutronix.de Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1t8cZ7-0003f5-95; Wed, 06 Nov 2024 10:43:05 +0100 Received: from pty.whiteo.stw.pengutronix.de ([2a0a:edc0:2:b01:1d::c5]) by drehscheibe.grey.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1t8cZ6-002HRH-0z; Wed, 06 Nov 2024 10:43:04 +0100 Received: from ore by pty.whiteo.stw.pengutronix.de with local (Exim 4.96) (envelope-from ) id 1t8cZ6-00HAnb-0e; Wed, 06 Nov 2024 10:43:04 +0100 Date: Wed, 6 Nov 2024 10:43:04 +0100 From: Oleksij Rempel To: Jiri Pirko Cc: Dmitry Antipov , Robin van der Gracht , Oliver Hartkopp , Marc Kleine-Budde , linux-can@vger.kernel.org, netdev@vger.kernel.org, lvc-project@linuxtesting.org, syzbot+d4e8dc385d9258220c31@syzkaller.appspotmail.com Subject: Re: [PATCH v2] can: fix skb reference counting in j1939_session_new() Message-ID: References: <20241105094823.2403806-1-dmantipov@yandex.ru> Precedence: bulk X-Mailing-List: linux-can@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: ore@pengutronix.de X-SA-Exim-Scanned: No (on metis.whiteo.stw.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-can@vger.kernel.org On Tue, Nov 05, 2024 at 05:37:53PM +0100, Jiri Pirko wrote: > Tue, Nov 05, 2024 at 10:48:23AM CET, dmantipov@yandex.ru wrote: > >Since 'j1939_session_skb_queue()' do an extra 'skb_get()' for each > >new skb, I assume that the same should be done for an initial one > > It is odd to write "I assume" for fix like this. You should know for > sure, don't you? Hm... looks the there is more then one refcounting problem at this point. skb_queue is set from 3 different paths, with resulting 3 different refcount states: j1939_sk_send_loop() skb = j1939_sk_alloc_skb() // skb with refcount == 1 if (!session) { session = j1939_tp_send(priv, skb, size) ... session = j1939_session_new(priv, skb, size); skb_queue_tail(&session->skb_queue, skb); // skb refcount == 1 } else { j1939_session_skb_queue(session, skb); // here, skb is refcounted skb_queue_tail(&session->skb_queue, skb_get(skb)); // skb refcount == 2 } // at the end of function, skb refcount == 1 or 2 j1939_xtp_rx_rts_session_new() j1939_session_fresh_new() skb = alloc_skb() // skb with refcount == 1 session = j1939_session_new(priv, skb, size); skb_queue_tail(&session->skb_queue, skb); skb_put(skb, size); // skb with refcount == 0 I agree with this patch, but there is missing skb_put() in j1939_sk_send_loop() > > >in 'j1939_session_new()' just to avoid refcount underflow. > > > >Reported-by: syzbot+d4e8dc385d9258220c31@syzkaller.appspotmail.com > >Closes: https://syzkaller.appspot.com/bug?extid=d4e8dc385d9258220c31 > >Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol") > >Signed-off-by: Dmitry Antipov > >--- > >v2: resend after hitting skb refcount underflow once again when looking > >around https://syzkaller.appspot.com/bug?extid=0e6ddb1ef80986bdfe64 > >--- > > net/can/j1939/transport.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > >diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c > >index 319f47df3330..95f7a7e65a73 100644 > >--- a/net/can/j1939/transport.c > >+++ b/net/can/j1939/transport.c > >@@ -1505,7 +1505,7 @@ static struct j1939_session *j1939_session_new(struct j1939_priv *priv, > > session->state = J1939_SESSION_NEW; > > > > skb_queue_head_init(&session->skb_queue); > >- skb_queue_tail(&session->skb_queue, skb); > >+ skb_queue_tail(&session->skb_queue, skb_get(skb)); > > > > skcb = j1939_skb_to_cb(skb); > > memcpy(&session->skcb, skcb, sizeof(session->skcb)); > >-- > >2.47.0 > > > > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |