[PATCH net] sctp: validate cached peer INIT chunk length in COOKIE_ECHO processing

When a listening SCTP server processes a COOKIE_ECHO chunk, the cached
peer INIT chunk embedded after the cookie is parsed and its parameters
are later walked by sctp_process_init() using sctp_walk_params().

However, the chunk header length of this cached INIT chunk was not
validated against the remaining buffer in the COOKIE_ECHO payload. If
the length field is inflated, the parameter walk can run beyond the
actual received data, leading to out-of-bounds reads and potential
memory corruption during later parameter handling (e.g. STATE_COOKIE
processing and kmemdup() copies).

Add a bounds check in sctp_unpack_cookie() to ensure the cached INIT
chunk length does not exceed the available data in the COOKIE_ECHO
buffer before it is used.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Brian Geffon <[email protected]>
Signed-off-by: Xin Long <[email protected]>
---
 net/sctp/sm_make_chunk.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index de86ac088289..85264862fb6b 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1730,6 +1730,7 @@ struct sctp_association *sctp_unpack_cookie(
 	struct sctp_signed_cookie *cookie;
 	struct sk_buff *skb = chunk->skb;
 	struct sctp_cookie *bear_cookie;
+	struct sctp_chunkhdr *ch;
 	enum sctp_scope scope;
 	unsigned int len;
 	ktime_t kt;
@@ -1759,6 +1760,10 @@ struct sctp_association *sctp_unpack_cookie(
 	cookie = chunk->subh.cookie_hdr;
 	bear_cookie = &cookie->c;
 
+	ch = (struct sctp_chunkhdr *)(bear_cookie + 1);
+	if (ntohs(ch->length) > len - fixed_size)
+		goto malformed;
+
 	/* Verify the cookie's MAC, if cookie authentication is enabled. */
 	if (sctp_sk(ep->base.sk)->cookie_auth_enable) {
 		u8 mac[SHA256_DIGEST_SIZE];
-- 
2.47.1