[PATCH net] calipso: keep BIG TCP payload_len in calipso_skbuff_setattr()

[Joas Antonio dos Santos <joasantonio108@gmail.com>]

calipso_skbuff_setattr() adjusts payload_len by the length of the
option it inserts or resizes:

	payload = ntohs(ip6_hdr->payload_len);
	ip6_hdr->payload_len = htons(payload + len_delta);

GRO can build BIG TCP packets larger than IPV6_MAXPLEN, and stores
payload_len == 0 for them; ipv6_payload_len() then falls back to
skb->len.  For such a packet forwarded to a destination mapped to
CALIPSO, the code above writes len_delta into payload_len, and
ipv6_payload_len() no longer falls back to skb->len.  nf_tables,
conntrack and sch_cake rely on it.

Leave payload_len alone when it is 0, as calipso_skbuff_delattr()
does.

Tested on one kernel (arm64, QEMU) with SELinux permissive, a minimal
mdp-generated policy (network_peer_controls=1), "netlabelctl calipso
add pass doi:16" and a default NetLabel mapping of fd00:2::/64 to
CALIPSO DOI 16:

- calipso_skbuff_setattr() called through netlbl_skbuff_setattr() from
  a test-only debugfs hook (not part of this patch, see below) on a
  70000 byte GSO TCPv6 skb with payload_len 0:

    before: payload_len 16, ipv6_payload_len() 16
    after:  payload_len 0,  ipv6_payload_len() 70016 (== skb->len - 40)

  and on a 1000 byte skb: payload_len 1000 -> 1016 both before and
  after.

- Forward path, client -> router -> server network namespaces, the
  client injects 5 unlabeled UDP datagrams with AF_PACKET (to avoid
  socket labeling): the router adds the CALIPSO option, the server sees
  nexthdr 0 with payload_len 31 (15 + 16) and delivers all 5 datagrams
  (Udp6InDatagrams 5, Ip6InTruncatedPkts 0), with and without this
  patch.

Fixes: 81fbc812132c ("ipv6/gro: insert temporary HBH/jumbo header")
Suggested-by: Eric Dumazet <edumazet@kernel.org>
Signed-off-by: Joas Antonio dos Santos <joasantonio108@gmail.com>
Assisted-by: Claude:claude-opus-5-5
---
This is the separate patch for calipso_skbuff_setattr() mentioned in
the review of "calipso: update payload_len when removing the CALIPSO
option".

Test-only debugfs hook used above (built in with obj-y in
net/netlabel/Makefile, triggered with
"echo 1 > /sys/kernel/debug/calipso_selftest"):

  // SPDX-License-Identifier: GPL-2.0
  /* TEST ONLY, not for submission: drive calipso_skbuff_setattr() through
   * netlbl_skbuff_setattr() with a normal and a BIG TCP sized skb.
   * Needs a NetLabel default mapping to CALIPSO (netlabelctl).
   * Trigger: echo 1 > /sys/kernel/debug/calipso_selftest
   */
  #include <linux/debugfs.h>
  #include <linux/ipv6.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <net/ipv6.h>
  #include <net/netlabel.h>

  static void run_one(const char *name, unsigned int payload, __be16 plen_field,
  		    bool gso)
  {
  	struct netlbl_lsm_secattr secattr;
  	struct ipv6hdr *ip6;
  	struct sk_buff *skb;
  	int rc;

  	skb = alloc_skb(LL_MAX_HEADER + 512 + sizeof(*ip6) + payload, GFP_KERNEL);
  	if (!skb)
  		return;
  	skb_reserve(skb, LL_MAX_HEADER + 512);
  	skb_reset_network_header(skb);
  	ip6 = skb_put_zero(skb, sizeof(*ip6) + payload);
  	ip6->version = 6;
  	ip6->nexthdr = IPPROTO_TCP;
  	ip6->hop_limit = 64;
  	ip6->payload_len = plen_field;
  	ipv6_addr_set(&ip6->saddr, htonl(0xfd000001), 0, 0, htonl(2));
  	ipv6_addr_set(&ip6->daddr, htonl(0xfd000002), 0, 0, htonl(2));
  	skb->protocol = htons(ETH_P_IPV6);
  	if (gso) {
  		/* what GRO builds for a BIG TCP aggregate */
  		skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
  		skb_shinfo(skb)->gso_size = 1400;
  	}

  	netlbl_secattr_init(&secattr);
  	secattr.flags = NETLBL_SECATTR_MLS_LVL;
  	secattr.attr.mls.lvl = 0;

  	pr_info("CALSELFTEST %s: before skb->len=%u payload_len=%u ipv6_payload_len=%u\n",
  		name, skb->len, ntohs(ipv6_hdr(skb)->payload_len),
  		ipv6_payload_len(skb, ipv6_hdr(skb)));
  	rc = netlbl_skbuff_setattr(skb, AF_INET6, &secattr);
  	pr_info("CALSELFTEST %s: after  rc=%d skb->len=%u nexthdr=%u payload_len=%u ipv6_payload_len=%u expected=%u\n",
  		name, rc, skb->len, ipv6_hdr(skb)->nexthdr,
  		ntohs(ipv6_hdr(skb)->payload_len),
  		ipv6_payload_len(skb, ipv6_hdr(skb)),
  		skb->len - (unsigned int)sizeof(struct ipv6hdr));

  	netlbl_secattr_destroy(&secattr);
  	kfree_skb(skb);
  }

  static ssize_t trigger(struct file *f, const char __user *buf, size_t len,
  		       loff_t *pos)
  {
  	run_one("normal", 1000, htons(1000), false);
  	run_one("bigtcp", 70000, 0, true);
  	return len;
  }

  static const struct file_operations fops = { .write = trigger };

  static int __init calipso_selftest_init(void)
  {
  	debugfs_create_file("calipso_selftest", 0200, NULL, NULL, &fops);
  	return 0;
  }
  late_initcall(calipso_selftest_init);

 net/ipv6/calipso.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/calipso.c b/net/ipv6/calipso.c
index c6a34334e..dfea7ed65 100644
--- a/net/ipv6/calipso.c
+++ b/net/ipv6/calipso.c
@@ -1318,7 +1318,7 @@ static int calipso_skbuff_setattr(struct sk_buff *skb,
 	struct ipv6hdr *ip6_hdr;
 	struct ipv6_opt_hdr *hop;
 	unsigned char buf[CALIPSO_MAX_BUFFER];
-	int len_delta, new_end, pad, payload;
+	int len_delta, new_end, pad;
 	unsigned int start, end;
 
 	ip6_hdr = ipv6_hdr(skb);
@@ -1357,8 +1357,9 @@ static int calipso_skbuff_setattr(struct sk_buff *skb,
 			sizeof(*ip6_hdr) + start);
 		skb_reset_network_header(skb);
 		ip6_hdr = ipv6_hdr(skb);
-		payload = ntohs(ip6_hdr->payload_len);
-		ip6_hdr->payload_len = htons(payload + len_delta);
+		/* BIG TCP packets have payload_len == 0 */
+		if (ip6_hdr->payload_len)
+			be16_add_cpu(&ip6_hdr->payload_len, len_delta);
 	}
 
 	hop = (struct ipv6_opt_hdr *)(ip6_hdr + 1);
-- 
2.43.0