From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=220.197.31.8 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793947329; b=Cmz2L+UriXqdw5K4hiXgAF3pwcna0O9O3WjDKueFY75Lh5/BgwF9qtwq5rrZ9LBtD1Tj OO7/BrnMsYl3BtoSmOaWyCyZWk9qECS4H3uuCdhaP0gVHrDBsB2AiXMyO2hZk87GwEhVd Y81UjxFqXmW2N4++74SeCMZNgw/yrpl2kU4GG2L03IfZa2Ber5B1E8daMp/xFayRstmmN Ld5qXSTP8CkF6MA4fcVP0BDi8UC1hX9cDFFcsQmyI2XreHqb9AsR/wkaSg+HzOfpsM2Eg rIpqErnaJn4U6iRrUL3lAYNPpiGbUlXb0jrPNtpCw7gw1eVMAZ2HEomYGcpI8i0TScQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793947329; h=DMARC-Filter:DKIM-Signature:Received:From:To:Cc:Subject:Date: Message-Id:X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding:X-CM-TRANSID:X-Coremail-Antispam: X-CM-SenderInfo; bh=KL5V+v3cUK42avBygg/NokDd0cEzHSdupAtDovHJxz0=; b=h3OvxF4zrjAUmUUQVwXNSZcm0ZdbpvVob0JXcWT24FXbO/91Lj6h3FZDm4Y9IZ8Ij9+U VDX76/gy454ff/u2+jXx0N+crcmAsszdL+md/v4JZk1mo9OS1zWS5oEbCX5CmE4Wf8AYI CUeUr/Q5tMdHkoijMF8yFrNFMWCZpPERv4J9/64CW0fBTfmqOUHszQSponybdYnZqUKpu Xmd39lTRg3HgAkVclU0vDQDfHCOJwhXzvww62nWsKt8ZMJuadSphxZRU3HPmIk/Jyn14I ukDdvib8cIg3Fbq7Tv5qoykOVDX92vnw+yoEr3slwoPJWuVun8u8d7FTvMESrYvWaOA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=126.com; spf=pass smtp.mailfrom=126.com; dkim=pass header.d=126.com header.i=@126.com header.a=rsa-sha256 header.s=s110527 header.b=fGhQ7jXb; arc=none smtp.remote-ip=220.197.31.8 Received: from m16.mail.126.com (m16.mail.126.com [220.197.31.8]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 03640606A335; Fri, 6 Nov 2026 06:42:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 03640606A335 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=126.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=126.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=126.com header.i=@126.com header.a=rsa-sha256 header.s=s110527 header.b=fGhQ7jXb DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=126.com; s=s110527; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=KL 5V+v3cUK42avBygg/NokDd0cEzHSdupAtDovHJxz0=; b=fGhQ7jXbQHVw0UGkPC ssOlfF5LBueH95TOQYsjOaGHMMpbXCISFsP/+Z7tqQCM0fgbDDDo8ZpQOhnC8reB w/LlG8i5BSQAXfGBUQk0nDJGO/5BJWBoGsbEyOVk539RR2Vjy2g5c/9srhtCG2XY TCWIGy+qmQE2+mYYgUPSnrnsw= Received: from localhost.localdomain (unknown []) by gzga-smtp-mtada-g0-4 (Coremail) with SMTP id _____wDnR+uMdu1qZ7kzCw--.3170S3; Fri, 06 Nov 2026 14:41:19 +0800 (CST) From: Linkui Xiao To: jhs@mojatatu.com, jiri@resnulli.us, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Linkui Xiao Subject: [PATCH net-next 1/3] net/sched: act_gact: size TCA_GACT_PROB unconditionally Date: Fri, 6 Nov 2026 14:41:12 +0800 Message-Id: <20261106064114.3592670-2-xiaolinkui@126.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20261106064114.3592670-1-xiaolinkui@126.com> References: <20261106064114.3592670-1-xiaolinkui@126.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wDnR+uMdu1qZ7kzCw--.3170S3 X-Coremail-Antispam: 1Uf129KBjvJXoWxWFWkZFWfGrWDWFWrXrWUJwb_yoW5tFWkpF Z8WayDCr1ktry7Xw48uw4xZa4S93s5CF4UWryakw1Fkr4kWwnxtFyrK3y3Cry7Grs3G3s5 Zr1qqr17GF9ruaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07U9AwsUUUUU= X-CM-SenderInfo: p0ld0z5lqn3xa6rslhhfrp/xtbBqA-WrWrtdo924QAA31 From: Linkui Xiao tcf_gact_get_fill_size() reads tcfg_ptype with neither tcfg_lock nor READ_ONCE(), and budgets TCA_GACT_PROB only when that read happens to be non-zero. Both halves are wrong. The bare read is a data race. tcf_gact_init() writes tcfg_ptype under spin_lock_bh(&gact->tcf_lock) when an action is replaced, tcf_gact_dump() re-reads it under the same lock, and tcf_gact_act() reads it with READ_ONCE(). get_fill_size() is the only accessor of the field with neither. act_bpf hit the same problem and solved it by taking tcf_lock in tcf_bpf_get_fill_size(), with a comment explaining why. The conditional budget breaks the rule that commit 4ba61bfd4998 ("net/sched: add get_fill_size() to the five actions that lack one") spells out: "Size every optional attribute unconditionally: reading the current flags to size it conditionally would race a concurrent replace, which can flip the attributes between sizing and dumping." A replace that turns tcfg_ptype from zero into non-zero between the two calls leaves tcf_gact_dump() writing a TCA_GACT_PROB attribute -- nla_total_size(sizeof(struct tc_gact_p)) == 12 bytes -- that was never budgeted. Size TCA_GACT_PROB unconditionally. The budget becomes an upper bound again and the bare read goes away, so unlike act_bpf this needs no lock. Nothing overflows today, so this is locking hygiene plus conformance to the rule above rather than a live bug. All four consumers of the value -- tcf_get_notify(), tcf_del_notify_msg(), tcf_add_notify_msg() and tcf_reoffload_del_notify_msg() -- allocate at least max(attr_size, NLMSG_GOODSIZE), and the delete and add paths add tcf_action_warn_attr_size(extack) on top. NLMSG_GOODSIZE is SKB_WITH_OVERHEAD(PAGE_SIZE), so a batch has to carry enough actions for attr_size to grow past roughly 3.7 KiB before a 12-byte shortfall matters -- which is the failure mode that commit 8e2efb3f45a5 ("net/sched: add get_fill_size callbacks for actions missing them") fixed for other actions. A replace cannot interleave between sizing and dumping either: RTM_NEWACTION, RTM_DELACTION and RTM_GETACTION all take rtnl, and the classifier path, which can run without rtnl, computes attr_size in tcf_exts_validate_ex() and discards it. Tested by building with CONFIG_GACT_PROB=y so that the code being changed is actually compiled; net/sched builds with W=1 and no new warnings. Patch 3 adds TDC cases for the gact dump and get paths. Fixes: 9c5c9c573700 ("net sched actions: implement get_fill_size routine in act_gact") Signed-off-by: Linkui Xiao --- net/sched/act_gact.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/sched/act_gact.c b/net/sched/act_gact.c index 565860cccba6..ec9a65dfc442 100644 --- a/net/sched/act_gact.c +++ b/net/sched/act_gact.c @@ -233,9 +233,10 @@ static size_t tcf_gact_get_fill_size(const struct tc_action *act) size_t sz = nla_total_size(sizeof(struct tc_gact)); /* TCA_GACT_PARMS */ #ifdef CONFIG_GACT_PROB - if (to_gact(act)->tcfg_ptype) - /* TCA_GACT_PROB */ - sz += nla_total_size(sizeof(struct tc_gact_p)); + /* tcfg_ptype may be set by a concurrent replace after this budget has + * been computed, so account for TCA_GACT_PROB unconditionally. + */ + sz += nla_total_size(sizeof(struct tc_gact_p)); #endif return sz; -- 2.25.1