From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0C0CC3C063F; Tue, 16 Jun 2026 16:42:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781628145; cv=none; b=GucOHzQt0URHPJ6PxJUS4jhL1OaRHpgD+jLh0r6tcN4rFLRoEXRuz1Sp5kPdkJNzlHbDR6uZ68xIWdUEnVnkUdYUu1bmPo4guCYKjZwy9U5tTb0w1/b1Ug07pQANI+PqADPCsjQB4SDDNF4gwZxvaUZBGFaz5jtobWGlJhNq0QA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781628145; c=relaxed/simple; bh=g4CrVNmz4hCMlfaVdXrSdPisUotc4fZPZ5mgv6SlHNo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PDxBjenw21l32bhmnDa+1iP1wPpDeK219Yod7mg8AOAxLyXVrukKc3bWUpsIe34gkkc9bE9fNgfCq1POnNWAWqtahBsm4d68RQhHQ/5NGg276dbLVZNPmLIBj3TrEVlRMiQcVTPFN7PZzXSSAx7nGwtgDVWAtHENzhKEJSYvyao= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=19Ahj9Zq; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="19Ahj9Zq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BFC691F000E9; Tue, 16 Jun 2026 16:42:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781628143; bh=b68tOxsnMYlhQseVcxGxOGfT8JvnZT+DDczKTHVom8E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=19Ahj9ZqZcXdwluxuXWEp8Ya+bt0JMzQSdYTqOjrLUJbm3mIU4c3F8ScO66vuYGsD 9f6VqQNcWHA89KF/rpYgOTFrWBjrpNqjaPu3pIvwULQCxCQB24w6keYV3n7bXpTh46 /WcYL4OgCImKMq/yXPpKIJbRGfPpWWJjTiNK8C/c= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Leo Lin , David Ahern , Steffen Klassert , Sasha Levin Subject: [PATCH 6.6 010/452] xfrm: Check for underflow in xfrm_state_mtu Date: Tue, 16 Jun 2026 20:23:57 +0530 Message-ID: <20260616145118.341195305@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145117.796205997@linuxfoundation.org> References: <20260616145117.796205997@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Ahern [ Upstream commit 742b04d0550b0ec89dcbc99537ec88653bd1ad90 ] Leo Lin reported OOB write issue in esp component: xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned modulo-2^32 space using an attacker-influenced "header_len + authsize + net_adj" subtracted from a small "mtu" argument. A nobody user can install an IPv4 ESP tunnel SA with a large authentication key (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc), configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a large value. When a single UDP datagram is then sent through the tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and esp_output() consumes it as a signed int via: padto = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached)) esp.tfclen = padto - skb->len (assigned to int) esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t when passed to memset() inside esp_output_fill_trailer(), producing a ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as "Write of size 18446744073709551537 at addr ffff888...". Check for underflow and return 1. This causes the sendmsg attempt to fail with ENETUNREACH. Fixes: c5c252389374 ("[XFRM]: Optimize MTU calculation") Reported-by: Leo Lin Assisted-by: Codex:26.506.31004 Signed-off-by: David Ahern Signed-off-by: Steffen Klassert Signed-off-by: Sasha Levin --- net/xfrm/xfrm_state.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 8ba31cf9b31993..6e8860779e2154 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -2860,10 +2860,14 @@ u32 xfrm_state_mtu(struct xfrm_state *x, int mtu) const struct xfrm_type *type = READ_ONCE(x->type); struct crypto_aead *aead; u32 blksize, net_adj = 0; + u32 overhead, payload_mtu; if (x->km.state != XFRM_STATE_VALID || - !type || type->proto != IPPROTO_ESP) + !type || type->proto != IPPROTO_ESP) { + if (mtu <= x->props.header_len) + return 1; return mtu - x->props.header_len; + } aead = x->data; blksize = ALIGN(crypto_aead_blocksize(aead), 4); @@ -2883,8 +2887,17 @@ u32 xfrm_state_mtu(struct xfrm_state *x, int mtu) break; } - return ((mtu - x->props.header_len - crypto_aead_authsize(aead) - - net_adj) & ~(blksize - 1)) + net_adj - 2; + overhead = x->props.header_len + crypto_aead_authsize(aead) + net_adj; + if (mtu <= overhead) + return 1; + + payload_mtu = mtu - overhead; + payload_mtu &= ~(blksize - 1); + if (payload_mtu <= 2) + return 1; + + return payload_mtu + net_adj - 2; + } EXPORT_SYMBOL_GPL(xfrm_state_mtu); -- 2.53.0