sctp: validate embedded INIT chunk and address list lengths in cookie

sctp: validate embedded INIT chunk and address list lengths in cookie

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@kernel.org>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/75af23a89adf881a0895d511775e4770da367cbf.1780873427.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>