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 E6FC1538D94; Wed, 23 Sep 2026 14:43:48 +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=1790174630; cv=none; b=u/hHGUluWXFQY2fW9949ppcEyhKMMlQ6ZQh8AAlsbaguHPRgBjvk0m/aehDOxqSVghaSiOAOIgQDz0LZV/2y47LgNsS3xKSUhBHg7OkxRjNIKseYQjXaJO6NRUwB/GR2vxGhCPhSt5RFyRHTaNPW9D1SJ5kzelTawIZswH55WYg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790174630; c=relaxed/simple; bh=kWEMnwaAhcV0fXkPaPsMN+Fjobck511nVI1VzGFLrMc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=owP3G5ozAiNjqcY9wWXHZh7Q6AH99bYwCZl3iOzsApA/ya5kAcfuPhSHXbtQTupZuRK9aKXznpEjxKeEPeyo8WcBckqzYCcRpExIg4Iy5zRhIb9lg/cyDLqqPSB2gMMkj21XbWdlfx8KMprTAKoam+ejcidc5VcpFtqascqk9Gs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=gfyci0RT; 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="gfyci0RT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4BC11F000FF; Wed, 23 Sep 2026 14:43:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790174627; bh=c1F6Ybdec4zALz2Ytwk/XZ99iqKOUj7DsUPjULcRln0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=gfyci0RT6SiEyMEn+cKZTtYPrcVYodZAplBcUeCvDaTSLf+5mmd+dUX0PEYCUTaEv SPg07P3rsUmQv4JVGrXzE+QwXG9Px9aZEBG21YTsQbHYBKtAciduHiOaJ1s63PapsG 4zw8WDwq0PIIJ0EWrodfw9nqWK4zVKUGcvNcgCBI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Eric Dumazet , Simon Horman , Paolo Abeni , Sasha Levin Subject: [PATCH 6.18 136/398] tcp: do not let tcp_rmem be set below 4096 Date: Wed, 23 Sep 2026 16:03:30 +0200 Message-ID: <20260923140646.959088336@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260923140643.441954610@linuxfoundation.org> References: <20260923140643.441954610@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: Eric Dumazet [ Upstream commit 83a945a529d6e002dd7339c532288a931f463dba ] We can hit a division by zero crash in tcp_rcvbuf_grow() and tcp_rcv_space_adjust(): divide error: 0000 [#1] PREEMPT SMP RIP: 0010:tcp_rcvbuf_grow+0x187/0x450 net/ipv4/tcp_input.c:939 ... grow = div_u64(((u64)rcvwin << 1) * (newval - oldval), oldval); The division uses oldval = tp->rcvq_space.space as divisor. When tp->rcvq_space.space is zero, this leads to a divide-by-zero exception. tp->rcvq_space.space is initialized in tcp_init_buffer_space(): tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd, (u32)TCP_INIT_CWND * tp->advmss); If tcp_rmem[1] is configured to very small values (such as 1), sk->sk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which computes (sk->sk_rcvbuf * scaling_ratio) >> 8, truncates to 0. This sets tp->window_clamp = 0, tp->rcv_ssthresh = 0, and tp->rcvq_space.space = 0. Later, when data arrives and DRS is invoked, tcp_rcvbuf_grow() divides by oldval == 0. Back in 2015, commit b1cb59cf2efe ("net: sysctl_net_core: check SNDBUF and RCVBUF for min length") ensured that net.core.rmem_default and net.core.rmem_max cannot be set below SOCK_MIN_RCVBUF. Similarly, SO_RCVBUF setsockopt enforces max_t(int, val * 2, SOCK_MIN_RCVBUF). However, net.ipv4.tcp_rmem still had .extra1 = SYSCTL_ONE, allowing arbitrarily small values. Because SOCK_MIN_RCVBUF depends on sizeof(struct sk_buff) and cacheline alignment, its value varies across architectures and configuration options. Using a fixed constant of 4096 ensures a predictable, architecture- independent lower bound that is safely above SOCK_MIN_RCVBUF everywhere and matches the documented 4K default. Fix this by setting tcp_rmem.extra1 to 4096 and updating the documentation. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260912144848.3448026-1-edumazet@google.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- Documentation/networking/ip-sysctl.rst | 2 ++ net/ipv4/sysctl_net_ipv4.c | 4 +++- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index e13131770fa0c..27a861053b2f5 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -844,6 +844,8 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max case this value is ignored. Default: between 131072 and 32MB, depending on RAM size. + Each of the three values cannot be set below 4096. + tcp_sack - BOOLEAN Enable select acknowledgments (SACKS). diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index afcbb9d48cfa2..34a8a932402d8 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -49,6 +49,8 @@ static int tcp_plb_max_cong_thresh = 256; static unsigned int tcp_tw_reuse_delay_max = TCP_PAWS_MSL * MSEC_PER_SEC; static int tcp_ecn_mode_max = 2; +static int tcp_min_rcvbuf = 4096; + /* obsolete */ static int sysctl_tcp_low_latency __read_mostly; @@ -1435,7 +1437,7 @@ static struct ctl_table ipv4_net_table[] = { .maxlen = sizeof(init_net.ipv4.sysctl_tcp_rmem), .mode = 0644, .proc_handler = proc_dointvec_minmax, - .extra1 = SYSCTL_ONE, + .extra1 = &tcp_min_rcvbuf, }, { .procname = "tcp_comp_sack_delay_ns", -- 2.53.0