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[81.185.160.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568a54e71sm17163243f8f.1.2025.06.18.09.57.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Jun 2025 09:57:26 -0700 (PDT) Date: Wed, 18 Jun 2025 18:57:24 +0200 From: Paul Chaignon To: Greg Kroah-Hartman Cc: stable@vger.kernel.org, Greg Kroah-Hartman , patches@lists.linux.dev, Daniel Borkmann , Jakub Kicinski , Sasha Levin Subject: Re: [PATCH 6.6 257/356] net: Fix checksum update for ILA adj-transport Message-ID: References: <20250617152338.212798615@linuxfoundation.org> <20250617152348.550981340@linuxfoundation.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250617152348.550981340@linuxfoundation.org> On Tue, Jun 17, 2025 at 05:26:12PM +0200, Greg Kroah-Hartman wrote: > 6.6-stable review patch. If anyone has any objections, please let me know. Not an objection per se, but I've sent the same backport at https://lore.kernel.org/stable/6520b247c2d367849f41689f71961e9741b1b7eb.1750168920.git.paul.chaignon@gmail.com/ The only difference is that I also backported the second patch in the series, which had a conflict. The backported patchset should apply on 6.1, 6.6, and 6.12. I hope that was the correct way to proceed :) > > ------------------ > > From: Paul Chaignon > > [ Upstream commit 6043b794c7668c19dabc4a93c75b924a19474d59 ] > > During ILA address translations, the L4 checksums can be handled in > different ways. One of them, adj-transport, consist in parsing the > transport layer and updating any found checksum. This logic relies on > inet_proto_csum_replace_by_diff and produces an incorrect skb->csum when > in state CHECKSUM_COMPLETE. > > This bug can be reproduced with a simple ILA to SIR mapping, assuming > packets are received with CHECKSUM_COMPLETE: > > $ ip a show dev eth0 > 14: eth0@if15: mtu 1500 qdisc noqueue state UP group default qlen 1000 > link/ether 62:ae:35:9e:0f:8d brd ff:ff:ff:ff:ff:ff link-netnsid 0 > inet6 3333:0:0:1::c078/64 scope global > valid_lft forever preferred_lft forever > inet6 fd00:10:244:1::c078/128 scope global nodad > valid_lft forever preferred_lft forever > inet6 fe80::60ae:35ff:fe9e:f8d/64 scope link proto kernel_ll > valid_lft forever preferred_lft forever > $ ip ila add loc_match fd00:10:244:1 loc 3333:0:0:1 \ > csum-mode adj-transport ident-type luid dev eth0 > > Then I hit [fd00:10:244:1::c078]:8000 with a server listening only on > [3333:0:0:1::c078]:8000. With the bug, the SYN packet is dropped with > SKB_DROP_REASON_TCP_CSUM after inet_proto_csum_replace_by_diff changed > skb->csum. The translation and drop are visible on pwru [1] traces: > > IFACE TUPLE FUNC > eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) ipv6_rcv > eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) ip6_rcv_core > eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) nf_hook_slow > eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) inet_proto_csum_replace_by_diff > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) tcp_v6_early_demux > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_route_input > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_input > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_input_finish > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_protocol_deliver_rcu > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) raw6_local_deliver > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ipv6_raw_deliver > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) tcp_v6_rcv > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) __skb_checksum_complete > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) kfree_skb_reason(SKB_DROP_REASON_TCP_CSUM) > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) skb_release_head_state > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) skb_release_data > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) skb_free_head > eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) kfree_skbmem > > This is happening because inet_proto_csum_replace_by_diff is updating > skb->csum when it shouldn't. The L4 checksum is updated such that it > "cancels" the IPv6 address change in terms of checksum computation, so > the impact on skb->csum is null. > > Note this would be different for an IPv4 packet since three fields > would be updated: the IPv4 address, the IP checksum, and the L4 > checksum. Two would cancel each other and skb->csum would still need > to be updated to take the L4 checksum change into account. > > This patch fixes it by passing an ipv6 flag to > inet_proto_csum_replace_by_diff, to skip the skb->csum update if we're > in the IPv6 case. Note the behavior of the only other user of > inet_proto_csum_replace_by_diff, the BPF subsystem, is left as is in > this patch and fixed in the subsequent patch. > > With the fix, using the reproduction from above, I can confirm > skb->csum is not touched by inet_proto_csum_replace_by_diff and the TCP > SYN proceeds to the application after the ILA translation. > > Link: https://github.com/cilium/pwru [1] > Fixes: 65d7ab8de582 ("net: Identifier Locator Addressing module") > Signed-off-by: Paul Chaignon > Acked-by: Daniel Borkmann > Link: https://patch.msgid.link/b5539869e3550d46068504feb02d37653d939c0b.1748509484.git.paul.chaignon@gmail.com > Signed-off-by: Jakub Kicinski > Signed-off-by: Sasha Levin > --- > include/net/checksum.h | 2 +- > net/core/filter.c | 2 +- > net/core/utils.c | 4 ++-- > net/ipv6/ila/ila_common.c | 6 +++--- > 4 files changed, 7 insertions(+), 7 deletions(-) > > diff --git a/include/net/checksum.h b/include/net/checksum.h > index 1338cb92c8e72..28b101f26636e 100644 > --- a/include/net/checksum.h > +++ b/include/net/checksum.h > @@ -158,7 +158,7 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, > const __be32 *from, const __be32 *to, > bool pseudohdr); > void inet_proto_csum_replace_by_diff(__sum16 *sum, struct sk_buff *skb, > - __wsum diff, bool pseudohdr); > + __wsum diff, bool pseudohdr, bool ipv6); > > static __always_inline > void inet_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb, > diff --git a/net/core/filter.c b/net/core/filter.c > index 5143c8a9e52ca..e92f3a9017bb4 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -1987,7 +1987,7 @@ BPF_CALL_5(bpf_l4_csum_replace, struct sk_buff *, skb, u32, offset, > if (unlikely(from != 0)) > return -EINVAL; > > - inet_proto_csum_replace_by_diff(ptr, skb, to, is_pseudo); > + inet_proto_csum_replace_by_diff(ptr, skb, to, is_pseudo, false); > break; > case 2: > inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo); > diff --git a/net/core/utils.c b/net/core/utils.c > index c994e95172acf..5895d034bf279 100644 > --- a/net/core/utils.c > +++ b/net/core/utils.c > @@ -473,11 +473,11 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, > EXPORT_SYMBOL(inet_proto_csum_replace16); > > void inet_proto_csum_replace_by_diff(__sum16 *sum, struct sk_buff *skb, > - __wsum diff, bool pseudohdr) > + __wsum diff, bool pseudohdr, bool ipv6) > { > if (skb->ip_summed != CHECKSUM_PARTIAL) { > csum_replace_by_diff(sum, diff); > - if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr) > + if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr && !ipv6) > skb->csum = ~csum_sub(diff, skb->csum); > } else if (pseudohdr) { > *sum = ~csum_fold(csum_add(diff, csum_unfold(*sum))); > diff --git a/net/ipv6/ila/ila_common.c b/net/ipv6/ila/ila_common.c > index 95e9146918cc6..b8d43ed4689db 100644 > --- a/net/ipv6/ila/ila_common.c > +++ b/net/ipv6/ila/ila_common.c > @@ -86,7 +86,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, > > diff = get_csum_diff(ip6h, p); > inet_proto_csum_replace_by_diff(&th->check, skb, > - diff, true); > + diff, true, true); > } > break; > case NEXTHDR_UDP: > @@ -97,7 +97,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, > if (uh->check || skb->ip_summed == CHECKSUM_PARTIAL) { > diff = get_csum_diff(ip6h, p); > inet_proto_csum_replace_by_diff(&uh->check, skb, > - diff, true); > + diff, true, true); > if (!uh->check) > uh->check = CSUM_MANGLED_0; > } > @@ -111,7 +111,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, > > diff = get_csum_diff(ip6h, p); > inet_proto_csum_replace_by_diff(&ih->icmp6_cksum, skb, > - diff, true); > + diff, true, true); > } > break; > } > -- > 2.39.5 > > >