sctp: reject stale cookies with mismatched verification tags

sctp_unpack_cookie() skips cookie expiration checks whenever an
association already exists.  This is broader than the exception in
RFC 9260 Section 5.2.4.

For an existing association, Section 5.2.4 permits an expired State
Cookie only when both Verification Tags in the cookie match the current
association.  Otherwise, the packet SHOULD be discarded and a Stale
Cookie ERROR MUST be sent.

The broad check lets an expired Action A restart cookie reach
sctp_sf_do_dupcook_a().  In a runtime test with the default 60 second
cookie lifetime, replaying such a cookie after 65 seconds returned a
COOKIE-ACK and restarted the association.

Check cookie expiration unless both Verification Tags match.  This
preserves the Action D exception for a lost COOKIE ACK while rejecting
expired cookies in all other cases.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20260723225623.2658868-1-yangyx22@mails.tsinghua.edu.cn
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 c02809264075fa1bf0b1b70406c6f0584cb1d61a..a1c0334a1038abdaa0feb70db8735c8027fb2faa 100644 (file)
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1802,9 +1802,9 @@ struct sctp_association *sctp_unpack_cookie(
                goto fail;
        }
 
-       /* Check to see if the cookie is stale.  If there is already
-        * an association, there is no need to check cookie's expiration
-        * for init collision case of lost COOKIE ACK.
+       /* Check to see if the cookie is stale.  RFC 9260 Section 5.2.4
+        * exempts an expired cookie only when both Verification Tags match
+        * the current association.
         * If skb has been timestamped, then use the stamp, otherwise
         * use current time.  This introduces a small possibility that
         * a cookie may be considered expired, but this would only slow
@@ -1815,7 +1815,10 @@ struct sctp_association *sctp_unpack_cookie(
        else
                kt = ktime_get_real();
 
-       if (!asoc && ktime_before(bear_cookie->expiration, kt)) {
+       if ((!asoc ||
+            asoc->c.my_vtag != bear_cookie->my_vtag ||
+            asoc->c.peer_vtag != bear_cookie->peer_vtag) &&
+           ktime_before(bear_cookie->expiration, kt)) {
                suseconds_t usecs = ktime_to_us(ktime_sub(kt, bear_cookie->expiration));
                __be32 n = htonl(usecs);