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 <bgeffon@google.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/eb60825fa22d6f9e663c7d4dbb69f397b5d34d42.1780362366.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index de86ac088289e899a2aa70f3db9fe7d338db1009..85264862fb6b6cd87f85dbbf88638cf1f6b9d387 100644 (file)
--- 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];