From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.199 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793765740; b=rpEG1mVk8lm2LwbmA2QZOaTb1crSCx69+6kv/33RDh2yS728A6zJGRFDfuRDz81q+PGJ BtdjOfqXBFiYdXiAj6+3YmupaYTm95XClEuTlyIQ8a6R59gfeq8RUZAlh1V+JqyqrPV9l eERWrW17hSZHEuHnIjpTeJuZ5bj4v8l2iFrnA9yzzP/+EHCGqXfnuAnU8h1Rewbg0Jhuq wtacD5Yh0QGMShVXD3nGSVlTeU1DxpWLRlWy8K/5y1dt6LNwE18lJr6NgnvSmy5lpybqG AuVWWgJx21pmno49x+33VuZfS3N7ZyFK/AzWSTlXZu4b4hJShG6QHSPmzK6GM2bWXAQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793765740; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=t33hTerwq+aQ3mBUBeIWL6pRcgQAoxI6zsMD8gzG6mU=; b=36xGL7PgcgzQgV6rH6hUmCDsJ95YJ/a296JbcJ0Gm6vRIWp5fPX4GB+WQrDBCLu4KQbt F4tQTfdCv89xKgAcOahFpQTfi2mKnulIxM2HvDYdPYOWX+dLyNmEs1QI1Z2oKWOhRUbIj 46laEpdWC6aLGFx/EGZZR6FTd2PCSHwnjoDLsELHy7YyLkDeXqxVJYsmClhYv5eLKNGQD zgVKTPPZXdrJL9XLucsFcXVGzIcoi1YaKhnIpCuLUci0EBaF/BxO3rTCR19xiDDKN4Lib avHpqvOD8T1M8FPHeX5SOo47B1cNoINZxRvinRylmwna7XfMDdY2FsyDANms4iz+CAw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Nm5tWPga; arc=none smtp.remote-ip=91.218.175.199 Received: from mta0.migadu.com (out-199.mta0.migadu.com [91.218.175.199]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2650E606A328 for ; Wed, 4 Nov 2026 04:15:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 2650E606A328 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Nm5tWPga X-Envelope-To: netdev@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=NxfwJu25c702HsG2QS65lReEnsmm0Rh4tGfKZ6I/Ny4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793765736; v=1; x=1794370536; b=Nm5tWPgalX68xFEfNNc38YSABIskZs6IG3VHTQJSocIT9xy+bmmlyDrpey5dO0uaTtE3Dxg2 FlByApCrm5HoyBCjsWmgB3rQSOmlqx8bwsHCmfr5IN1jMcByvHN5l+GVTlUDRCh840ayfel0S83 2LguG0x76ctHm9JLCq0RQ8t4= X-Envelope-To: netdev@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 4202d724f29ea87b; Wed, 04 Nov 2026 04:15:23 +0000 X-Mizu-Trace-ID: 4202d724f29ea87b X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 4 Nov 2026 12:15:08 +0800 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v4 1/7] ipv6: treat a negative optlen as 4 in do_ipv6_getsockopt() To: Breno Leitao , David Ahern , Ido Schimmel , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , John Fastabend , Stanislav Fomichev , Shuah Khan , Eric Dumazet Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, david.laight.linux@gmail.com, kernel-team@meta.com References: <20261103-sockopt_expand_out_v2-v4-0-2d36da923578@debian.org> <20261103-sockopt_expand_out_v2-v4-1-2d36da923578@debian.org> From: Jiayuan Chen In-Reply-To: <20261103-sockopt_expand_out_v2-v4-1-2d36da923578@debian.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/3/26 7:01 PM, Breno Leitao wrote: > do_ipv6_getsockopt() reads optlen into an int and never checks its > sign. Most of what consumes len compares it as unsigned, so a negative > optlen reads as a huge buffer, and the reply depends on the option. > > The int options clamp it to their own size: > > len = min_t(unsigned int, sizeof(int), len); > > so getsockopt(fd, SOL_IPV6, IPV6_TCLASS, buf, &len) with len set to -1 > answers 4 bytes and reports 4, rather than failing. > > The other options see a huge buffer. The sticky options reply with > their whole header, IPV6_2292PKTOPTIONS writes every pending control > message without a limit, and IPV6_PATHMTU and IPV6_FLOWLABEL_MGR pass > their length check. > > do_ip_getsockopt() rejects a negative optlen, but doing that here would > turn a call that works today into an error for a caller that passes an > uninitialized length. Answer it as 4, as the int options do, for every > option this function handles itself. > > That leaves the int options as they are. The sticky headers are cut to > 4 bytes, IPV6_2292PKTOPTIONS gets a 4 byte control buffer, and > IPV6_PATHMTU and IPV6_FLOWLABEL_MGR fail with -EINVAL, as they do for > any other undersized buffer. > > MRT6_* is dispatched earlier and keeps rejecting a negative optlen, and > the netfilter fallback still sees the caller's value. > > This changes what callers that pass a negative length see. It is a > behaviour change, not a fix, so there is no Fixes: tag. > > The conversion of this function to sockopt_t builds its buffers from > optlen, which the standard helpers reject when negative, so the answer > has to be settled before that. > > Suggested-by: David Laight > Acked-by: Stanislav Fomichev > Acked-by: Ido Schimmel > Signed-off-by: Breno Leitao Reviewed-by: Jiayuan Chen > --- > net/ipv6/ipv6_sockglue.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c > index 4b3536571c9804..700133e2fd11c2 100644 > --- a/net/ipv6/ipv6_sockglue.c > +++ b/net/ipv6/ipv6_sockglue.c > @@ -1002,6 +1002,11 @@ int do_ipv6_getsockopt(struct sock *sk, int level, int optname, > > if (copy_from_sockptr(&len, optlen, sizeof(int))) > return -EFAULT; > + /* Historic bug compatibility: take a negative optlen as 4, as the > + * int options always did. > + */ > + if (len < 0) > + len = 4; > switch (optname) { > case MCAST_MSFILTER: > if (in_compat_syscall()) >