From: Yuxiang Yang Date: Thu, 23 Jul 2026 22:56:23 +0000 (+0000) Subject: sctp: reject stale cookies with mismatched verification tags X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9d8da8e0a9bce4a340af60dd0446bc7eb8d07587;p=thirdparty%2Fkernel%2Fstable.git 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 Acked-by: Xin Long Link: https://patch.msgid.link/20260723225623.2658868-1-yangyx22@mails.tsinghua.edu.cn Signed-off-by: Jakub Kicinski --- diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c index c02809264075..a1c0334a1038 100644 --- 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);