[PATCH] ipv6: calipso: fix 8-bit hdrlen overflow and missing pskb_may_pull() in hop-by-hop options

[Hui Peng <benquike@gmail.com>]

Two bugs exist in the CALIPSO hop-by-hop option handling in
net/ipv6/calipso.c:

1. When inserting a CALIPSO option into an existing Hop-by-Hop extension
   header in calipso_opt_insert() or calipso_skbuff_setattr(), the
   resulting header length `buf_len` (or `ipv6_optlen(hop) + len_delta`)
   can exceed the maximum size representable by the 8-bit `hdrlen` field
   (256 * 8 = 2048 bytes). When `buf_len > 2048`, `new->hdrlen = buf_len
   / 8 - 1` (or `hop->hdrlen = ...`) truncates modulo 256, causing
   `ipv6_optlen()` to under-report the allocated header size and
   mismatch `opt->opt_nflen` or `skb->len`.
2. In calipso_skbuff_setattr(), when `ip6_hdr->nexthdr == NEXTHDR_HOP`,
   `hop` is dereferenced at `(struct ipv6_opt_hdr *)(ip6_hdr + 1)` and
   scanned by `calipso_opt_find(hop, &start, &end)` without ensuring
   that the Hop-by-Hop header resides in the linear data area of `skb`
   via `pskb_may_pull()`, risking an out-of-bounds read past `skb->tail`
   on non-linear skbs.

Reject Hop-by-Hop headers that would exceed `8 * 256` bytes with
`-ENOSPC`, and ensure `pskb_may_pull()` linearizes `hop` before
inspecting it in calipso_skbuff_setattr().

Fixes: ceba1832b1b2 ("calipso: Set the calipso socket label to match the secattr.")
Fixes: 2917f57b6bc1 ("calipso: Allow the lsm to label the skbuff directly.")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>

---
 net/ipv6/calipso.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/ipv6/calipso.c b/net/ipv6/calipso.c
index c6a34334e657..b8b7451a16ed 100644
--- a/net/ipv6/calipso.c
+++ b/net/ipv6/calipso.c
@@ -944,6 +944,10 @@ calipso_opt_insert(struct ipv6_opt_hdr *hop,
 		memcpy((char *)new + buf_len, (char *)hop + end, hop_len - end);
 		buf_len += hop_len - end;
 	}
+	if (buf_len > 8 * 256) {
+		kfree(new);
+		return ERR_PTR(-ENOSPC);
+	}
 	new->nexthdr = 0;
 	new->hdrlen = buf_len / 8 - 1;
 
@@ -1323,6 +1327,13 @@ static int calipso_skbuff_setattr(struct sk_buff *skb,
 
 	ip6_hdr = ipv6_hdr(skb);
 	if (ip6_hdr->nexthdr == NEXTHDR_HOP) {
+		if (!pskb_may_pull(skb, sizeof(*ip6_hdr) + sizeof(*hop)))
+			return -EINVAL;
+		ip6_hdr = ipv6_hdr(skb);
+		hop = (struct ipv6_opt_hdr *)(ip6_hdr + 1);
+		if (!pskb_may_pull(skb, sizeof(*ip6_hdr) + ipv6_optlen(hop)))
+			return -EINVAL;
+		ip6_hdr = ipv6_hdr(skb);
 		hop = (struct ipv6_opt_hdr *)(ip6_hdr + 1);
 		ret_val = calipso_opt_find(hop, &start, &end);
 		if (ret_val && ret_val != -ENOENT)
@@ -1341,6 +1352,8 @@ static int calipso_skbuff_setattr(struct sk_buff *skb,
 	/* At this point new_end aligns to 4n, so (new_end & 4) pads to 8n */
 	pad = ((new_end & 4) + (end & 7)) & 7;
 	len_delta = new_end - (int)end + pad;
+	if (start && (int)ipv6_optlen(hop) + len_delta > 8 * 256)
+		return -ENOSPC;
 	ret_val = skb_cow(skb,
 			  skb_headroom(skb) + (len_delta > 0 ? len_delta : 0));
 	if (ret_val < 0)
-- 
2.55.0.1082.g2b9226bbc0-goog