[SRU][N][PATCH 1/1] sctp: validate embedded INIT chunk and address list lengths in cookie

[Cengiz Can]

From: Xin Long <lucien.xin at gmail.com>

sctp_unpack_cookie() only checked that the embedded INIT chunk length
did not exceed the remaining cookie payload, but did not ensure that the
INIT chunk is large enough to contain a complete INIT header.

A malformed COOKIE_ECHO can therefore carry a truncated INIT chunk whose
length field is smaller than sizeof(struct sctp_init_chunk).  Later,
sctp_process_init() accesses INIT parameters unconditionally, which may
lead to out-of-bounds reads.

In addition, raw_addr_list_len is not fully validated against the
remaining cookie payload. When cookie authentication is disabled, an
attacker can supply an oversized raw_addr_list_len and cause
sctp_raw_to_bind_addrs() to read beyond the end of the cookie. The
address parser also lacks sufficient bounds checks for parameter headers
and lengths, allowing malformed address parameters to trigger
out-of-bounds reads.

Fix this by:

- requiring the embedded INIT chunk length to be at least sizeof(struct
  sctp_init_chunk);
- validating that the INIT chunk and raw address list together fit
  within the cookie payload;
- verifying sufficient data exists for each address parameter header and
  payload before parsing it.

Note that sctp_verify_init() must be called after sctp_unpack_cookie()
and before sctp_process_init() when cookie authentication is disabled.
This will be addressed in a separate patch.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Sashiko <sashiko-bot at kernel.org>
Signed-off-by: Xin Long <lucien.xin at gmail.com>
Link: https://patch.msgid.link/75af23a89adf881a0895d511775e4770da367cbf.1780873427.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(backported from commit 6f4c80a2a7e6d06753b89a578b710a2499a5e62b)
[bot_kybele: This tree's sctp_unpack_cookie() lacked the original
 ch/ntohs(ch->length) bounds check that upstream modified, so git am
 fuzzy-matched the incoming block onto the "if (!sctp_sk(ep->base.sk)->hmac)
 goto no_hmac;" line; I added the full validation block (ch, chlen, INIT-size,
 raw_addr_list_len checks) before the MAC check and preserved the hmac goto
 no_hmac path.]
CVE-2026-53224
Assisted-by: kybele:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 net/sctp/bind_addr.c     | 11 ++++++++++-
 net/sctp/sm_make_chunk.c | 13 ++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/net/sctp/bind_addr.c b/net/sctp/bind_addr.c
index 6b95d3ba8fe1..0947b276d1e0 100644
--- a/net/sctp/bind_addr.c
+++ b/net/sctp/bind_addr.c
@@ -275,6 +275,16 @@ int sctp_raw_to_bind_addrs(struct sctp_bind_addr *bp, __u8 *raw_addr_list,
 		param = (struct sctp_paramhdr *)raw_addr_list;
 		rawaddr = (union sctp_addr_param *)raw_addr_list;
 
+		if (addrs_len < sizeof(*param)) {
+			retval = -EINVAL;
+			goto out_err;
+		}
+		len = ntohs(param->length);
+		if (addrs_len < len) {
+			retval = -EINVAL;
+			goto out_err;
+		}
+
 		af = sctp_get_af_specific(param_type2af(param->type));
 		if (unlikely(!af) ||
 		    !af->from_addr_param(&addr, rawaddr, htons(port), 0)) {
@@ -291,7 +301,6 @@ int sctp_raw_to_bind_addrs(struct sctp_bind_addr *bp, __u8 *raw_addr_list,
 			goto out_err;
 
 next:
-		len = ntohs(param->length);
 		addrs_len -= len;
 		raw_addr_list += len;
 	}
diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 96ca400120e6..d3cc4f5189fc 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1750,8 +1750,9 @@ struct sctp_association *sctp_unpack_cookie(
 	struct sk_buff *skb = chunk->skb;
 	struct sctp_cookie *bear_cookie;
 	__u8 *digest = ep->digest;
+	struct sctp_chunkhdr *ch;
+	unsigned int len, chlen;
 	enum sctp_scope scope;
-	unsigned int len;
 	ktime_t kt;
 
 	/* Header size is static data prior to the actual cookie, including
@@ -1779,6 +1780,16 @@ struct sctp_association *sctp_unpack_cookie(
 	cookie = chunk->subh.cookie_hdr;
 	bear_cookie = &cookie->c;
 
+	ch = (struct sctp_chunkhdr *)(bear_cookie + 1);
+	chlen = ntohs(ch->length);
+	if (chlen < sizeof(struct sctp_init_chunk))
+		goto malformed;
+	if (chlen > len - fixed_size)
+		goto malformed;
+	if (bear_cookie->raw_addr_list_len > len - fixed_size - chlen)
+		goto malformed;
+
+	/* Verify the cookie's MAC, if cookie authentication is enabled. */
 	if (!sctp_sk(ep->base.sk)->hmac)
 		goto no_hmac;
 
-- 
2.43.0