From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f173.google.com (mail-pg1-f173.google.com [209.85.215.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8BD0B377020 for ; Sun, 12 Apr 2026 11:11:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775992283; cv=none; b=iF7QEM8B6eM4Avao9IDYaAHnhw8ptolGoKZ6aK0eUvOMB0Dmd0jIhLBswbJNz0R1b/Msiezqfaga6zBTgi4xnrWkPv40P+8SXX4ek6XeH+3Xzu6LlE5PGwWhplI7BQfFwtJXapTCBmj7sRZGCl6wtrysl4qufXGdlN03hGVvULE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775992283; c=relaxed/simple; bh=dj8E8sQuMvGGkeFgw8ZCRE6siDsAKhcLUq+TYgXiQ34=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MB0GrzeCOPIx8IJynOLPxSSTECOK7cDAJ8f8n77Ar+st7a1LdZEErF1MajhkAjNgaVDH/QAGtqy9xT8F9UoJFlzYuFzLEXzCOUuafGrnYZouXPz91hhZ1OJM2SpiNrGYmQb+fogLQvT+C9NLGc5LS8sIi2AHT0FkHt8zOk9W6lY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=IGI7LEN9; arc=none smtp.client-ip=209.85.215.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="IGI7LEN9" Received: by mail-pg1-f173.google.com with SMTP id 41be03b00d2f7-c742d4df00cso1252910a12.1 for ; Sun, 12 Apr 2026 04:11:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1775992282; x=1776597082; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=I5YffUmzhaIkIbUoe3E2/Xuq3wXpeEBIn/sASnY+Ntk=; b=IGI7LEN9sfwwrFbqoegKXUcHxc/hWXDY1cz/df+uA7X+miZZ0+LNhgnjzS+7Xd31A3 V1jj8a9aRrz7qtWWrNK3p1r1Sj/S0OTu9T5JtOOn55JOE95uUZo679GolGKyFwMmEFst dkduT2MnXg5kgQdIVoi8agfkMJTpqF6QQdjctCtisDwhDCBxwYXj7goltFto63abH8nR Xjz9EZhXJczu0KVbpXNGACZoGVbH95dxOwU5nI8Uh4sXBsCWNDuqummwCXYtA+8vkN18 oIoc5K1aQgDGZ5F4AkA1REC53jzKbEs2FJClY63VXIqHGaxUTh+hUvZ7YDUxVVl6yyBG BJTA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775992282; x=1776597082; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=I5YffUmzhaIkIbUoe3E2/Xuq3wXpeEBIn/sASnY+Ntk=; b=pl/8SW2z0AectbxTAmz77PkFEO4aRcN/xGCtsd8cILjMhEFEycYsXo+++avjVOBuFY tA2ipGv4ZQItVJlNzh/ADbv5F5yDmCM/9x68hWFXI6vE5Vrk5PP02W6GP7JqlCjMhyQn WoxH6oHIX5e1HtRd4oPRS/+Pt0ZcnW6O9a1Sh/HToz6c8uKRnWISEXW/aRivrOQSEFM4 PREzTXLkh5ae0IujHOhdaUPMoAdRJEGCv91EwmWsOQTyV4yhJQZK1Dc+PN4Izq+VqmTr /vqVBxbvWudbMl+yh8692pymwEhVVFO5kY/SIk+ghzkeMpt3bKu7FjttyeRu8twcFx+U N46Q== X-Forwarded-Encrypted: i=1; AJvYcCXITXzcE5mNzr/+UgwXO/vFLIS0K+TaxiuIYOZf+rKKx5pA4neg6f/geBGJ3SYN5XbDnJob+0R56ozanvU=@vger.kernel.org X-Gm-Message-State: AOJu0YxlL7BUgFPensmMCG+mE0qySwiEE2xxuwf9ow37eAeaEjocZE1I T2IDclFObyoJRCAaBM6GbQMM1pBquxuhTDp/ae2W6rZHlXQEZZa8+KeG7PnIHkSGw7s= X-Gm-Gg: AeBDietEmCPWl2fMp9e3Zlqd8iKIoWNDWMO/g+FC8Q56WeHREdVjyBDFoJt38IFe4+6 Sf4nAvBgO0uDrnURVq2DZ8+ydEZLvqYrR2Cmt5XhLSx791cyv+ugbnItunoT0fHrssraOPN941P 7plMI6eFFsdA8P3133vuXNVkVcOEZqV92DmuMY2Wz01i5KUa8MrlzIDHGuD94oRMC+Pt/89GEim TWPhwBFWMlhcMJ6ihwtxVgNv5O7QVJl7Hrwi7luXWh5MMXg2fzdxLZxfNGe4T16ms/+pIm4oSux Z64qOR+PMKcwUvM/vTw/1je7kgKNCj+iuu4ebPNS/QUwwl4WBAAeR97WAgHZqyLVLKN3cshdeNP vnVaHpSu6cz10oePv/jLU4c9zzcjTwdJXrZ2FK40hvHYkI46njOeTwI1Swjx+/8JG+BcXBDQ7eE 6602WkY3bnJlSsQ2Iaonj+kpEmD6+U6GbMT1u4ESjA X-Received: by 2002:a05:6a20:3d87:b0:398:7667:b2fb with SMTP id adf61e73a8af0-39fe466bbd7mr8477194637.19.1775992281819; Sun, 12 Apr 2026 04:11:21 -0700 (PDT) Received: from DESKTOP-82PPU4A.localdomain ([202.8.116.169]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c7934c9ef38sm2522981a12.12.2026.04.12.04.11.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 12 Apr 2026 04:11:21 -0700 (PDT) From: Ujjal Roy To: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Nikolay Aleksandrov , Ido Schimmel , David Ahern , Shuah Khan , Andy Roulin , Yong Wang , Petr Machata Cc: Ujjal Roy , bridge@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net-next v4 3/5] ipv4: igmp: encode multicast exponential fields Date: Sun, 12 Apr 2026 11:10:45 +0000 Message-ID: <20260412111047.1326-4-royujjal@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260412111047.1326-1-royujjal@gmail.com> References: <20260412111047.1326-1-royujjal@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In IGMP, MRC and QQIC fields are not correctly encoded when generating query packets. Since the receiver of the query interprets these fields using the IGMPv3 floating- point decoding logic, any value that exceeds the linear threshold is incorrectly parsed as an exponential value, leading to an incorrect interval calculation. Encode and assign the corresponding protocol fields during query generation. Introduce the logic to dynamically calculate the exponent and mantissa using bit-scan (fls). This ensures MRC and QQIC fields (8-bit) are properly encoded when transmitting query packets with intervals that exceed their respective linear threshold value of 128 (for MRT/QQI). RFC3376: for both MRC and QQIC, values >= 128 represent the same floating-point encoding as follows: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |1| exp | mant | +-+-+-+-+-+-+-+-+ Signed-off-by: Ujjal Roy --- include/linux/igmp.h | 87 +++++++++++++++++++++++++++++++++++++++ net/bridge/br_multicast.c | 14 +++---- 2 files changed, 93 insertions(+), 8 deletions(-) diff --git a/include/linux/igmp.h b/include/linux/igmp.h index 4443c914b3c8..4d8af9031e18 100644 --- a/include/linux/igmp.h +++ b/include/linux/igmp.h @@ -109,6 +109,93 @@ struct ip_mc_list { /* IGMPV3 floating-point exponential field threshold */ #define IGMPV3_EXP_MIN_THRESHOLD 128 +/* Max representable (mant = 0xF, exp = 7) -> 31744 */ +#define IGMPV3_EXP_MAX_THRESHOLD 31744 + +/* V3 exponential field encoding */ + +/* IGMPv3 MRC/QQIC 8-bit exponential field encode + * + * RFC3376, 4.1.1 & 4.1.7. defines only the decoding formula: + * MRT/QQI = (mant | 0x10) << (exp + 3) + * + * but does NOT define the encoding procedure. To derive exponent: + * + * For any value of mantissa and exponent, the decoding formula + * indicates that the "hidden bit" (0x10) is shifted 4 bits left + * to sit above the 4-bit mantissa. The RFC again shifts this + * entire block left by (exp + 3) to reconstruct the value. + * So, 'hidden bit' is the MSB which is shifted by (4 + exp + 3). + * + * Total left shift of the 'hidden bit' = 4 + (exp + 3) = exp + 7. + * This is the MSB at the 0-based bit position: (exp + 7). + * Since fls() is 1-based, fls(value) - 1 = exp + 7. + * + * Therefore: + * exp = fls(value) - 8 + * mant = (value >> (exp + 3)) & 0x0F + * + * Final encoding formula: + * 0x80 | (exp << 4) | mant + * + * Example (value = 3200): + * 0 1 + * 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * |0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0| (value = 3200) + * | ^-^-mant^ ^..(exp+3)..^| exp = 4, mant = 9 + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * + * Encoded: + * 0x80 | (4 << 4) | 9 = 0xC9 + */ +static inline u8 igmpv3_exp_field_encode(unsigned long value) +{ + u8 mc_exp, mc_man; + + /* MRC/QQIC < 128 is literal */ + if (value < IGMPV3_EXP_MIN_THRESHOLD) + return value; + + /* Saturate at max representable (mant = 0xF, exp = 7) -> 31744 */ + if (value >= IGMPV3_EXP_MAX_THRESHOLD) + return 0xFF; + + mc_exp = fls(value) - 8; + mc_man = (value >> (mc_exp + 3)) & 0x0F; + + return 0x80 | (mc_exp << 4) | mc_man; +} + +/* Calculate Maximum Response Code from Max Resp Time + * + * RFC3376, relevant sections: + * - 4.1.1. Maximum Response Code + * - 8.3. Query Response Interval + * + * MRC represents the encoded form of Max Resp Time (MRT); once + * decoded, the resulting value is in units of 0.1 seconds (100 ms). + */ +static inline u8 igmpv3_mrc(unsigned long mrt) +{ + return igmpv3_exp_field_encode(mrt); +} + +/* Calculate Querier's Query Interval Code from Querier's Query Interval + * + * RFC3376, relevant sections: + * - 4.1.7. QQIC (Querier's Query Interval Code) + * - 8.2. Query Interval + * - 8.12. Older Version Querier Present Timeout + * (the [Query Interval] in the last Query received) + * + * QQIC represents the encoded form of Querier's Query Interval (QQI); + * once decoded, the resulting value is in units of seconds. + */ +static inline u8 igmpv3_qqic(unsigned long qi) +{ + return igmpv3_exp_field_encode(qi); +} /* V3 exponential field decoding */ diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 1438c023db62..27010744d7ae 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -934,12 +934,12 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm size_t pkt_size, igmp_hdr_size; unsigned long now = jiffies; struct igmpv3_query *ihv3; + unsigned long lmqt, mrt; void *csum_start = NULL; __sum16 *csum = NULL; struct sk_buff *skb; struct igmphdr *ih; struct ethhdr *eth; - unsigned long lmqt; struct iphdr *iph; u16 lmqt_srcs = 0; @@ -1004,15 +1004,15 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm skb_put(skb, 24); skb_set_transport_header(skb, skb->len); + mrt = group ? brmctx->multicast_last_member_interval : + brmctx->multicast_query_response_interval; *igmp_type = IGMP_HOST_MEMBERSHIP_QUERY; switch (brmctx->multicast_igmp_version) { case 2: ih = igmp_hdr(skb); ih->type = IGMP_HOST_MEMBERSHIP_QUERY; - ih->code = (group ? brmctx->multicast_last_member_interval : - brmctx->multicast_query_response_interval) / - (HZ / IGMP_TIMER_SCALE); + ih->code = mrt / (HZ / IGMP_TIMER_SCALE); ih->group = group; ih->csum = 0; csum = &ih->csum; @@ -1021,11 +1021,9 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm case 3: ihv3 = igmpv3_query_hdr(skb); ihv3->type = IGMP_HOST_MEMBERSHIP_QUERY; - ihv3->code = (group ? brmctx->multicast_last_member_interval : - brmctx->multicast_query_response_interval) / - (HZ / IGMP_TIMER_SCALE); + ihv3->code = igmpv3_mrc(mrt / (HZ / IGMP_TIMER_SCALE)); ihv3->group = group; - ihv3->qqic = brmctx->multicast_query_interval / HZ; + ihv3->qqic = igmpv3_qqic(brmctx->multicast_query_interval / HZ); ihv3->nsrcs = htons(lmqt_srcs); ihv3->resv = 0; ihv3->suppress = sflag; -- 2.43.0