Merge branch 'net-fix-inet_proto_csum_replace_by_diff-for-ipv6'

Paul Chaignon says:

====================
net: Fix inet_proto_csum_replace_by_diff for IPv6

This patchset fixes a bug that causes skb->csum to hold an incorrect
value when calling inet_proto_csum_replace_by_diff for an IPv6 packet
in CHECKSUM_COMPLETE state. This bug affects BPF helper
bpf_l4_csum_replace and IPv6 ILA in adj-transport mode.

In those cases, inet_proto_csum_replace_by_diff updates the L4 checksum
field after an IPv6 address change. These two changes cancel each other
in terms of checksum, so skb->csum shouldn't be updated.

v2: https://lore.kernel.org/[email protected]
====================

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

include/net/checksum.h

@@ -152,7 +152,7 @@ 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,

include/uapi/linux/bpf.h

@@ -2056,6 +2056,7 @@ union bpf_attr {
  * 		for updates resulting in a null checksum the value is set to
  * 		**CSUM_MANGLED_0** instead. Flag **BPF_F_PSEUDO_HDR** indicates
  * 		that the modified header field is part of the pseudo-header.
+ * 		Flag **BPF_F_IPV6** should be set for IPv6 packets.
  *
  * 		This helper works in combination with **bpf_csum_diff**\ (),
  * 		which does not update the checksum in-place, but offers more
@@ -6072,6 +6073,7 @@ enum {
 	BPF_F_PSEUDO_HDR		= (1ULL << 4),
 	BPF_F_MARK_MANGLED_0		= (1ULL << 5),
 	BPF_F_MARK_ENFORCE		= (1ULL << 6),
+	BPF_F_IPV6			= (1ULL << 7),
 };
 
 /* BPF_FUNC_skb_set_tunnel_key and BPF_FUNC_skb_get_tunnel_key flags. */

net/core/filter.c

@@ -1968,10 +1968,11 @@ BPF_CALL_5(bpf_l4_csum_replace, struct sk_buff *, skb, u32, offset,
 	bool is_pseudo = flags & BPF_F_PSEUDO_HDR;
 	bool is_mmzero = flags & BPF_F_MARK_MANGLED_0;
 	bool do_mforce = flags & BPF_F_MARK_ENFORCE;
+	bool is_ipv6   = flags & BPF_F_IPV6;
 	__sum16 *ptr;
 
 	if (unlikely(flags & ~(BPF_F_MARK_MANGLED_0 | BPF_F_MARK_ENFORCE |
-			       BPF_F_PSEUDO_HDR | BPF_F_HDR_FIELD_MASK)))
+			       BPF_F_PSEUDO_HDR | BPF_F_HDR_FIELD_MASK | BPF_F_IPV6)))
 		return -EINVAL;
 	if (unlikely(offset > 0xffff || offset & 1))
 		return -EFAULT;
@@ -1987,7 +1988,7 @@ 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, is_ipv6);
 		break;
 	case 2:
 		inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo);

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)));

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;
 	}

tools/include/uapi/linux/bpf.h

@@ -2056,6 +2056,7 @@ union bpf_attr {
  * 		for updates resulting in a null checksum the value is set to
  * 		**CSUM_MANGLED_0** instead. Flag **BPF_F_PSEUDO_HDR** indicates
  * 		that the modified header field is part of the pseudo-header.
+ * 		Flag **BPF_F_IPV6** should be set for IPv6 packets.
  *
  * 		This helper works in combination with **bpf_csum_diff**\ (),
  * 		which does not update the checksum in-place, but offers more
@@ -6072,6 +6073,7 @@ enum {
 	BPF_F_PSEUDO_HDR		= (1ULL << 4),
 	BPF_F_MARK_MANGLED_0		= (1ULL << 5),
 	BPF_F_MARK_ENFORCE		= (1ULL << 6),
+	BPF_F_IPV6			= (1ULL << 7),
 };
 
 /* BPF_FUNC_skb_set_tunnel_key and BPF_FUNC_skb_get_tunnel_key flags. */