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 C92611DE8AE; Sun, 7 Jun 2026 10:09:47 +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=1780826988; cv=none; b=oAFxWRrzEcoGZTLyfXQiJ1t01TIK9leAueBLlbyM5tVZ6UaWCu4Dz8fFdsKE6givUumdGJJkj9xi4tnKSwf2lE4v45BUPtPm47AGYzl+7nYoyYKtsVWAKCz1C/mbAGZXNGSJ/jpeimYu/DAmBUdk+PEQTxSFgywzaSIBAj+CeYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780826988; c=relaxed/simple; bh=BLS6S/7FxlHFqJnRhm4lPhH399omtoER/AvxHD4dxNI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lQm6RXi/QpS3vR/90OAszDrbMDHRb2RfhUfRaUFsLPYBFF5ME00QgIOo9WHfjJEfHi2mi7guORbfqULerZPPyuviyoXJAwIDUbyrrYntvlQ2sSvkUV3WsvQey9V3U516LrD4BREB6TsHA3xp/M48Hx74nz+g7LV4lzJRNjLKO8Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=WoZLkG2z; 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="WoZLkG2z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29FE61F00893; Sun, 7 Jun 2026 10:09:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780826987; bh=osCT1OFlpKgTazNObqSyHHVg/wm+9i3SVJWngFxXXMY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=WoZLkG2zkYfgMaw/OD4LMNGKIUuZ82ow2xwrH5EHAwj6uVZBqILDPmSnnAUHBf+Wv mFQ6EUsCiqlr7AX41OeoI7iXOroLyEvFnHxXkb0D7BWmaCap8+anJPIZOLOfCnl3SX 7Ryw9qwLL1kiuPot/XSQh7nNzonCORYk39Djrt+I= 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 6.18 009/315] xfrm: Check for underflow in xfrm_state_mtu Date: Sun, 7 Jun 2026 11:56:36 +0200 Message-ID: <20260607095727.849611722@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095727.528828913@linuxfoundation.org> References: <20260607095727.528828913@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 6.18-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 f6ba58f18ac18e..1b81e92e3eee78 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -3113,10 +3113,14 @@ 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); @@ -3139,8 +3143,17 @@ 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