From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from plesk.hostmyservers.fr (plesk.hostmyservers.fr [45.145.164.37]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BB9E21E1C1F; Tue, 8 Apr 2025 15:58:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.145.164.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744127925; cv=none; b=htjORQf6VJfAgkoTIYE6U+fdDZ+E2GeLTHDGkULLgFPhEnRI7MWsmCZ8xBdYuuMTSIoS3P20a5CINSW/+sv9X4HTNdudr67tLDVWov1mqNmuEXUDwJqLoKPvaxwzghdnMzwtCpff704bAdBeEoUrRqS336OPwasHhTgH5E2IccU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744127925; c=relaxed/simple; bh=AHvLh3VHhH+8s0BqalzzLWIJRhM0DmQZyfPUYf0ycCM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hVNstmxSrRMkXQthLuXagu9ik3f5sxKPbhSoKEHO0t2yYuISfHl9GKwrDHImH8vVKDhGTI+UdH1vwLXVIV+vR4gEPYI1Rn3wVohdbAqVs8t73KKsNymPUqFxCUrBbnH+NMGp+63r7h67anNd7J1F40xEl+iciKq+ymUM6oDm4tk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com; spf=pass smtp.mailfrom=arnaud-lcm.com; arc=none smtp.client-ip=45.145.164.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arnaud-lcm.com Received: from [IPV6:2a01:e0a:3e8:c0d0:9059:1ccf:a15c:f330] (unknown [IPv6:2a01:e0a:3e8:c0d0:9059:1ccf:a15c:f330]) by plesk.hostmyservers.fr (Postfix) with ESMTPSA id 36E84487F4; Tue, 8 Apr 2025 15:58:40 +0000 (UTC) Authentication-Results: Plesk; spf=pass (sender IP is 2a01:e0a:3e8:c0d0:9059:1ccf:a15c:f330) smtp.mailfrom=contact@arnaud-lcm.com smtp.helo=[IPV6:2a01:e0a:3e8:c0d0:9059:1ccf:a15c:f330] Received-SPF: pass (Plesk: connection is authenticated) Message-ID: Date: Tue, 8 Apr 2025 17:58:39 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] net: ppp: Add bound checking for skb d on ppp_sync_txmung To: Simon Horman Cc: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-ppp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, syzbot+29fc8991b0ecb186cf40@syzkaller.appspotmail.com References: <20250407-bound-checking-ppp_txmung-v1-1-cfcd2efe39e3@arnaud-lcm.com> <20250408153352.GY395307@horms.kernel.org> Content-Language: en-US From: Arnaud Lecomte In-Reply-To: <20250408153352.GY395307@horms.kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-PPP-Message-ID: <174412792069.11363.17962374028464217077@Plesk> X-PPP-Vhost: arnaud-lcm.com Thanks for the review. You're right, using a merge commit in the `Fixes:` tag was not relevant. I'll send a v2 shortly with the fix as well as the removal of the skb check as it is already done before. On 08/04/2025 17:33, Simon Horman wrote: > On Mon, Apr 07, 2025 at 05:26:21PM +0200, Arnaud Lecomte wrote: >> Ensure we have enough data in linear buffer from skb before accessing >> initial bytes. This prevents potential out-of-bounds accesses >> when processing short packets. >> >> When ppp_sync_txmung receives an incoming package with an empty >> payload: >> (remote) gef➤ p *(struct pppoe_hdr *) (skb->head + skb->network_header) >> $18 = { >> type = 0x1, >> ver = 0x1, >> code = 0x0, >> sid = 0x2, >> length = 0x0, >> tag = 0xffff8880371cdb96 >> } >> >> from the skb struct (trimmed) >> tail = 0x16, >> end = 0x140, >> head = 0xffff88803346f400 "4", >> data = 0xffff88803346f416 ":\377", >> truesize = 0x380, >> len = 0x0, >> data_len = 0x0, >> mac_len = 0xe, >> hdr_len = 0x0, >> >> it is not safe to access data[2]. >> >> Reported-by: syzbot+29fc8991b0ecb186cf40@syzkaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40 >> Tested-by: syzbot+29fc8991b0ecb186cf40@syzkaller.appspotmail.com >> Fixes: 9946eaf552b1 ("Merge tag 'hardening-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux") > It doesn't seem right to use a Merge commit in a fixes tag. > > Looking over the code, the access to data[2] seems to have existed since > the beginning of git history, in which case I think we can use this: > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > >> Signed-off-by: Arnaud Lecomte >> --- >> drivers/net/ppp/ppp_synctty.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c >> index 644e99fc3623..520d895acc60 100644 >> --- a/drivers/net/ppp/ppp_synctty.c >> +++ b/drivers/net/ppp/ppp_synctty.c >> @@ -506,6 +506,11 @@ ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb) >> unsigned char *data; >> int islcp; >> >> + /* Ensure we can safely access protocol field and LCP code */ >> + if (!skb || !pskb_may_pull(skb, 3)) { > I doubt that skb can be NULL. > >> + kfree_skb(skb); >> + return NULL; >> + } >> data = skb->data; >> proto = get_unaligned_be16(data); >> >> >> --- >> base-commit: 9946eaf552b194bb352c2945b54ff98c8193b3f1 >> change-id: 20250405-bound-checking-ppp_txmung-4807c854ed85 >> >> Best regards, >> -- >> Arnaud Lecomte >> >>