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 37735478E57; Sat, 12 Sep 2026 11:37:51 +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=1789213073; cv=none; b=TemTJIHFwDmwCn+2A1nJpB2b7bEeD2SsrTFUyhJx2Z+euERDC4b3JGAvP3grM4GEWgW6CH621w2sngM6yiVm5sQ2SrTMX+6gNFgKaecfMr3oLsUbJnnmnSHV4YGbdjZtKRn9LMfnJXUEkqYkxGi7ojVMG6aoB7psKzg7RKFq6EY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789213073; c=relaxed/simple; bh=JvAZLIXPlONUYeISrnQFsa4Tv8LQlCqGUtbjMqJSF5I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ncmWfT7Osvjl+m9XGZfhM2GF/+ijTFjCjhX8aLjeNHjn/PKZftDgbfEH6TiRh0fZIW+GWg5hj5hlm8JMXQF2bAgCi4BTaBgxRiUnpYrB+vzHH7Khc1Ik1o3KqOollq7lU81FrWU/TjUjJH00Py1IsuIgvuAQZ+iebJyJYJ33M7Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=scCFAE+f; 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="scCFAE+f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02E511F000FF; Sat, 12 Sep 2026 11:37:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789213071; bh=QwfVfGoLuM+F9Ar/zsM6Zp+Act80R7+Ay1XfFaNRHZI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=scCFAE+foym2VYyjKo2AUugtIfEMDkS9381x6WDz0caW+ixpaC9qMskzHHutgTL6j Pt3AqnYKmbrQ9/3sjLjcCjwRE27CW516o/UVGAYWVPHeR1bKkK64I8hJ3pGO8TJ1yp dtWRz58rTF7U9qxrEY+MeL1TcYQOc0OkqL/QsJQA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Maciej Fijalkowski , Jason Xing , Stanislav Fomichev , Jakub Kicinski , Suraj Jitindar Singh , Sasha Levin Subject: [PATCH 6.12 0005/1376] xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata() Date: Sat, 12 Sep 2026 08:40:31 +0200 Message-ID: <20260912065607.667647307@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065607.535295758@linuxfoundation.org> References: <20260912065607.535295758@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jason Xing commit 22ba97ea9cc1f63a0d0244fae38057ed452b6ac7 upstream. The TX metadata area resides in the UMEM buffer which is memory-mapped and concurrently writable by userspace. In xsk_skb_metadata(), csum_start and csum_offset are read from shared memory for bounds validation, then read again for skb assignment. A malicious userspace application can race to overwrite these values between the two reads, bypassing the bounds check and causing out-of-bounds memory access during checksum computation in the transmit path. Fix this by reading csum_start and csum_offset into local variables once, then using the local copies for both validation and assignment. Note that other metadata fields (flags, launch_time) and the cached csum fields may be mutually inconsistent due to concurrent userspace writes, but this is benign: the only security-critical invariant is that each field's validated value is the same one used, which local caching guarantees. Closes: https://lore.kernel.org/all/20260503200927.73EA1C2BCB4@smtp.kernel.org/ Reviewed-by: Maciej Fijalkowski Signed-off-by: Jason Xing Acked-by: Stanislav Fomichev Fixes: 48eb03dd2630 ("xsk: Add TX timestamp and TX checksum offload support") Link: https://patch.msgid.link/20260530042630.80626-1-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski [ 6.12: Apply fix in xsk_build_skb() since missing patch 30c3055f9c0d ("xsk: wrap generic metadata handling onto separate function") added in v6.18 which moves handling to separate function xsk_skb_metadata(). ] Signed-off-by: Suraj Jitindar Singh Signed-off-by: Sasha Levin --- net/xdp/xsk.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index da7e11e3bfad2..76675ce70f03d 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -665,6 +665,7 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, struct xsk_tx_metadata *meta = NULL; struct net_device *dev = xs->dev; struct sk_buff *skb = xs->skb; + u16 csum_start, csum_offset; bool first_frag = false; int err; @@ -733,15 +734,17 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, } if (meta->flags & XDP_TXMD_FLAGS_CHECKSUM) { - if (unlikely(meta->request.csum_start + - meta->request.csum_offset + + csum_start = READ_ONCE(meta->request.csum_start); + csum_offset = READ_ONCE(meta->request.csum_offset); + + if (unlikely(csum_start + csum_offset + sizeof(__sum16) > len)) { err = -EINVAL; goto free_err; } - skb->csum_start = hr + meta->request.csum_start; - skb->csum_offset = meta->request.csum_offset; + skb->csum_start = hr + csum_start; + skb->csum_offset = csum_offset; skb->ip_summed = CHECKSUM_PARTIAL; if (unlikely(xs->pool->tx_sw_csum)) { -- 2.53.0