From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [91.216.245.30]) (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 71AF13DF011 for ; Tue, 7 Jul 2026 11:18:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.216.245.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783423104; cv=none; b=bU6JVbMLkll/ZpRPjykQU5v9dgVpWNUiO+SHNOGmUqdjnLDsIqD1z5PW45cWV6VZGf5yR7EeHGwzCht8owK0SkNxnirMIp3unvy/2wgv/jZjhqdPtC0lUih/8UCa/0xjmkyPmRZHJDJzunhMo5Tjm8UvQ9uUcGpwHaB5Bx+97vw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783423104; c=relaxed/simple; bh=a1wlmx9a3eyKnO28RETCiDXd0YlBm1f55iTucryzmzA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=KB4tKdBRy3ASMqLkB4F1TVli8Klo0rWKxZtExJEASIWds9W1ugEv3sRxTz8b+Dzyt+4euvGPG78082AJaUhmmJKEtI60P+bMi/5YsBCCH/fZIviAeNB3a0XHzRP0QJ24KMLVzoZcLPmXgE8bwAZACaAnm9XaD9bHGCAj2ZghtNM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de; spf=pass smtp.mailfrom=Chamillionaire.breakpoint.cc; arc=none smtp.client-ip=91.216.245.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=Chamillionaire.breakpoint.cc Received: by Chamillionaire.breakpoint.cc (Postfix, from userid 1003) id 357C16047A; Tue, 07 Jul 2026 13:18:20 +0200 (CEST) From: Florian Westphal To: Cc: Florian Westphal , Mina Almasry Subject: [PATCH nf v2] netfilter: handle unreadable frags Date: Tue, 7 Jul 2026 13:18:08 +0200 Message-ID: <20260707111808.15057-1-fw@strlen.de> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit sashiko reports: When an skb with unreadable fragments (such as from devmem TCP, where skb_frags_readable(skb) returns false) is processed by the u32 module, skb_copy_bits() will safely return a negative error code [..] xt_u32: bail out with hotdrop in this case. gather_frags: return -1, just as if we had no fragment header. nfnetlink_queue: restrict to the non-linear part. nfnetlink_log: restrict to the non-linear part. v2: - skb_zerocopy helpers don't copy readable flag, i.e. nfnetlink_queue is broken too xt_u32 shouldn't return true if hotdrop was set. Cc: Mina Almasry Fixes: 65249feb6b3d ("net: add support for skbs with unreadable frags") Signed-off-by: Florian Westphal --- Mina, there are other places that BUG on skb_copy_bits(). Could you please have a look at: https://sashiko.dev/#/patchset/20260706155219.23757-1-fw%40strlen.de and see if those need fixing or not? [ and the v2 review of this ... ] Also, should skb_zerocopy() copy over the skb->readable flag (or refuse to handle unreadable skbs)? net/ipv6/netfilter/nf_conntrack_reasm.c | 2 +- net/netfilter/nfnetlink_log.c | 26 ++++++++++++++++--------- net/netfilter/nfnetlink_queue.c | 16 +++++++++++---- net/netfilter/xt_u32.c | 16 ++++++++++----- 4 files changed, 41 insertions(+), 19 deletions(-) diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c index 3637b20d3fa4..599c49bf0a0a 100644 --- a/net/ipv6/netfilter/nf_conntrack_reasm.c +++ b/net/ipv6/netfilter/nf_conntrack_reasm.c @@ -419,7 +419,7 @@ find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff) return -1; } if (skb_copy_bits(skb, start, &hdr, sizeof(hdr))) - BUG(); + return -1; if (nexthdr == NEXTHDR_AUTH) hdrlen = ipv6_authlen(&hdr); else diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c index fa3657599861..6d1ed48c5e8f 100644 --- a/net/netfilter/nfnetlink_log.c +++ b/net/netfilter/nfnetlink_log.c @@ -676,7 +676,7 @@ __build_packet_message(struct nfnl_log_net *log, goto nla_put_failure; if (skb_copy_bits(skb, 0, nla_data(nla), data_len)) - BUG(); + goto nla_put_failure; } nlh->nlmsg_len = inst->skb->tail - old_tail; @@ -698,6 +698,21 @@ static const struct nf_loginfo default_loginfo = { }, }; +static unsigned int nfulnl_get_copy_len(const struct nf_loginfo *li, + const struct sk_buff *skb, + unsigned int copy_len) +{ + unsigned int len = skb->len; + + if ((li->u.ulog.flags & NF_LOG_F_COPY_LEN) && + li->u.ulog.copy_len < copy_len) + copy_len = li->u.ulog.copy_len; + if (!skb_frags_readable(skb)) + len = skb_headlen(skb); + + return min(len, copy_len); +} + /* log handler for internal netfilter logging api */ static void nfulnl_log_packet(struct net *net, @@ -790,14 +805,7 @@ nfulnl_log_packet(struct net *net, break; case NFULNL_COPY_PACKET: - data_len = inst->copy_range; - if ((li->u.ulog.flags & NF_LOG_F_COPY_LEN) && - (li->u.ulog.copy_len < data_len)) - data_len = li->u.ulog.copy_len; - - if (data_len > skb->len) - data_len = skb->len; - + data_len = nfulnl_get_copy_len(li, skb, inst->copy_range); size += nla_total_size(data_len); break; diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c index 35d4c6c628ff..b8aaf39cb4d8 100644 --- a/net/netfilter/nfnetlink_queue.c +++ b/net/netfilter/nfnetlink_queue.c @@ -690,6 +690,17 @@ static int nfqnl_put_master_ifindex(struct sk_buff *nlskb, int attr, } #endif +static unsigned int nfqnl_get_data_len(const struct sk_buff *entskb, + unsigned int copy_range) +{ + unsigned int data_len = entskb->len; + + if (!skb_frags_readable(entskb)) + data_len = skb_headlen(entskb); + + return min(data_len, copy_range); +} + static struct sk_buff * nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue, struct nf_queue_entry *entry, @@ -755,10 +766,7 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue, nf_queue_checksum_help(entskb)) return NULL; - data_len = READ_ONCE(queue->copy_range); - if (data_len > entskb->len) - data_len = entskb->len; - + data_len = nfqnl_get_data_len(entskb, READ_ONCE(queue->copy_range)); hlen = skb_zerocopy_headlen(entskb); hlen = min_t(unsigned int, hlen, data_len); size += sizeof(struct nlattr) + hlen; diff --git a/net/netfilter/xt_u32.c b/net/netfilter/xt_u32.c index ec1a21e3b6e2..dabbaa742874 100644 --- a/net/netfilter/xt_u32.c +++ b/net/netfilter/xt_u32.c @@ -14,8 +14,8 @@ #include #include -static bool u32_match_it(const struct xt_u32 *data, - const struct sk_buff *skb) +static int u32_match_it(const struct xt_u32 *data, + const struct sk_buff *skb) { const struct xt_u32_test *ct; unsigned int testind; @@ -40,7 +40,8 @@ static bool u32_match_it(const struct xt_u32 *data, return false; if (skb_copy_bits(skb, pos, &n, sizeof(n)) < 0) - BUG(); + return -1; + val = ntohl(n); nnums = ct->nnums; @@ -68,7 +69,7 @@ static bool u32_match_it(const struct xt_u32 *data, if (skb_copy_bits(skb, at + pos, &n, sizeof(n)) < 0) - BUG(); + return -1; val = ntohl(n); break; } @@ -90,9 +91,14 @@ static bool u32_match_it(const struct xt_u32 *data, static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par) { const struct xt_u32 *data = par->matchinfo; - bool ret; + int ret; ret = u32_match_it(data, skb); + if (ret < 0) { + par->hotdrop = true; + return false; + } + return ret ^ data->invert; } -- 2.54.0