From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (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 B5CCF35CBAF for ; Wed, 12 Nov 2025 23:24:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762989854; cv=none; b=b7D7ih/1K2CXZd8xnVnTB5R3jUk0THmJLgJPDBfHL6b3ANl/bI1gbKuznCIzriPMsZfQ914+8D4NB+8XzCuSp62aAzc2e+hj3zlCgF3mC+fE010xDqswLTBwIyaTEy15m5eDvbFeQXHomX8eOMoPSQqhbwtk5aOSqd2+X1Y/Mjo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762989854; c=relaxed/simple; bh=/rrqrWefr6Be8/0xwOqC6LYKV/EgTwyOcbreEBWCCuM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Sn8XYzPEc0vLv2j4VzrUIJ8pBM5D9USl5FRpWVtCjDUt4W5gEh6Y0lXQVEqQIt80kbPcz6oM2MwsrTsW0IoBb8ZFw4/I30CSVyA/pUJQjKoW2ltRn/82nEUta4hq1glHAdhpbJaKl0Bug9TPZpOQoP7sfeHSsIOxJ+9e+OviPIk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=FtabXl5d; arc=none smtp.client-ip=95.215.58.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="FtabXl5d" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1762989847; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Ae3Y9wLC7e7ztA80BXItavwEzFGlDsl4crb0Mx/OgXA=; b=FtabXl5dLrk+jCbT6Y9bZm8NdSH0StZRFNjxqiKkDpSgpmpCI9EB50QX4Dwn2Mh/JQDXhq uWDxxdkvrvANJfd10xVkxqTeU50xPvEzJiajee/TgnLeecoyB+rnHi0QW2bzmewAZ/LdaZ YW/WvQwZILBFJcHBucFPNmuRsQgSvtQ= From: Martin KaFai Lau To: bpf@vger.kernel.org Cc: 'Alexei Starovoitov ' , 'Andrii Nakryiko ' , 'Daniel Borkmann ' , netdev@vger.kernel.org, Jesper Dangaard Brouer , Kaiyan Mei , Yinhao Hu Subject: [PATCH bpf-next 1/2] bpf: Check skb->transport_header is set in bpf_skb_check_mtu Date: Wed, 12 Nov 2025 15:23:30 -0800 Message-ID: <20251112232331.1566074-1-martin.lau@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Martin KaFai Lau The bpf_skb_check_mtu helper needs to use skb->transport_header when the BPF_MTU_CHK_SEGS flag is used: bpf_skb_check_mtu(skb, ifindex, &mtu_len, 0, BPF_MTU_CHK_SEGS) The transport_header is not always set. There is a WARN_ON_ONCE report when CONFIG_DEBUG_NET is enabled + skb->gso_size is set + bpf_prog_test_run is used: WARNING: CPU: 1 PID: 2216 at ./include/linux/skbuff.h:3071 skb_gso_validate_network_len bpf_skb_check_mtu bpf_prog_3920e25740a41171_tc_chk_segs_flag # A test in the next patch bpf_test_run bpf_prog_test_run_skb For a normal ingress skb (not test_run), skb_reset_transport_header is performed but there is plan to avoid setting it as described in commit 2170a1f09148 ("net: no longer reset transport_header in __netif_receive_skb_core()"). This patch fixes the bpf helper by checking skb_transport_header_was_set(). The check is done just before skb->transport_header is used, to avoid breaking the existing bpf prog. The WARN_ON_ONCE is limited to bpf_prog_test_run, so targeting bpf-next. Fixes: 34b2021cc616 ("bpf: Add BPF-helper for MTU checking") Cc: Jesper Dangaard Brouer Reported-by: Kaiyan Mei Reported-by: Yinhao Hu Signed-off-by: Martin KaFai Lau --- net/core/filter.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 1efec0d70d78..df6ce85e48dc 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6429,9 +6429,12 @@ BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb, */ if (skb_is_gso(skb)) { ret = BPF_MTU_CHK_RET_SUCCESS; - if (flags & BPF_MTU_CHK_SEGS && - !skb_gso_validate_network_len(skb, mtu)) - ret = BPF_MTU_CHK_RET_SEGS_TOOBIG; + if (flags & BPF_MTU_CHK_SEGS) { + if (!skb_transport_header_was_set(skb)) + return -EINVAL; + if (!skb_gso_validate_network_len(skb, mtu)) + ret = BPF_MTU_CHK_RET_SEGS_TOOBIG; + } } out: *mtu_len = mtu; -- 2.47.3