From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 53F833DD858; Tue, 12 May 2026 17:54:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778608497; cv=none; b=U5E0nmjPiYcMWXZb9evuObIymnGzdzzSIiXc4ssMC8qdWR8XG/TseD8Dqvm4RWeYedh5dNAVDdsvq85mj+7UKnMCqTwwxHAStKlDephD9L/eSQmfLOMmgoLF/dAnsBy7EkMIOiT2noxXIMXBYqs6qoAGKXJ8ktxYxZmYCsk1Liw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778608497; c=relaxed/simple; bh=PyYm+Y3e0cwcZ8dUCvFfAqWvZZaKpJXRdHaxiWyjJIM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=T6nPSrVW7I6WSGXe4xwFs16u3EC3FaCcbFa/lyFUCLW5ho0aY5G2OL9m5GWydEURuxPNqD23VIsoaL6r643lUGwAt/g28F9ZBDcJwCoeP919ZUuL/D6ZDgTm9IBmDdQ5RARV94l+KxIYDDsXzGJSgiOxLIoPTwzTNwOPalMZ0Xc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=nSJ45QH3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="nSJ45QH3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E003AC2BCF5; Tue, 12 May 2026 17:54:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1778608497; bh=PyYm+Y3e0cwcZ8dUCvFfAqWvZZaKpJXRdHaxiWyjJIM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nSJ45QH3N1ViDfhP/3fWcb7WQln8itEWZjCyQnTJCtOOdz1eYVen148qGDWx4h7ku EqyaWZ+t+tzYfFRSEQ18azRQDfHqCrIKdpvQE8rLiVM3adepwaKSiHWQ4eslHeLldz m/oTqbgsP9u4w1QJZdL34EyqunL3PCnW1Hki8NxU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Breno Leitao , Jakub Kicinski Subject: [PATCH 6.18 102/270] netpoll: pass buffer size to egress_dev() to avoid MAC truncation Date: Tue, 12 May 2026 19:38:23 +0200 Message-ID: <20260512173940.606021397@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260512173938.452574370@linuxfoundation.org> References: <20260512173938.452574370@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: Breno Leitao commit 76b93a8107574006b25495664304ea9237494d70 upstream. egress_dev() formats np->dev_mac via snprintf() but receives buf as a bare char *, so it cannot derive the buffer size from the pointer. The size argument was hardcoded to MAC_ADDR_STR_LEN (3 * ETH_ALEN - 1 = 17), which is silly wrong in two ways: 1) misleading kernel log output on the MAC-selected target path (np->dev_name[0] == '\0'); for example "aa:bb:cc:dd:ee:ff doesn't exist, aborting" was logged as "aa:bb:cc:dd:ee:f doesn't exist, aborting". 2) the second argument of snprintf is the size of the buffer, not the size of what you want to write. Add a bufsz parameter to egress_dev() and pass sizeof(buf) from each caller, matching the standard snprintf() idiom and removing the hardcoded size from the helper. Every caller already declares "char buf[MAC_ADDR_STR_LEN + 1]" so the formatted MAC continues to fit. Tested by booting with netconsole=6665@/aa:bb:cc:dd:ee:ff,6666@10.0.0.1/00:11:22:33:44:55 on a kernel without a matching device. Pre-fix dmesg shows "aa:bb:cc:dd:ee:f doesn't exist, aborting"; post-fix shows the full "aa:bb:cc:dd:ee:ff doesn't exist, aborting". Fixes: f8a10bed32f5 ("netconsole: allow selection of egress interface via MAC address") Cc: stable@vger.kernel.org Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20260501-netpoll_snprintf_fix-v1-1-84b0566e6597@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/core/netpoll.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -608,14 +608,16 @@ EXPORT_SYMBOL_GPL(__netpoll_setup); /* * Returns a pointer to a string representation of the identifier used * to select the egress interface for the given netpoll instance. buf - * must be a buffer of length at least MAC_ADDR_STR_LEN + 1. + * is used to format np->dev_mac when np->dev_name is empty; bufsz must + * be at least MAC_ADDR_STR_LEN + 1 to fit the formatted MAC address + * and its NUL terminator. */ -static char *egress_dev(struct netpoll *np, char *buf) +static char *egress_dev(struct netpoll *np, char *buf, size_t bufsz) { if (np->dev_name[0]) return np->dev_name; - snprintf(buf, MAC_ADDR_STR_LEN, "%pM", np->dev_mac); + snprintf(buf, bufsz, "%pM", np->dev_mac); return buf; } @@ -645,7 +647,7 @@ static int netpoll_take_ipv6(struct netp if (!IS_ENABLED(CONFIG_IPV6)) { np_err(np, "IPv6 is not supported %s, aborting\n", - egress_dev(np, buf)); + egress_dev(np, buf, sizeof(buf))); return -EINVAL; } @@ -667,7 +669,7 @@ static int netpoll_take_ipv6(struct netp } if (err) { np_err(np, "no IPv6 address for %s, aborting\n", - egress_dev(np, buf)); + egress_dev(np, buf, sizeof(buf))); return err; } @@ -687,14 +689,14 @@ static int netpoll_take_ipv4(struct netp in_dev = __in_dev_get_rtnl(ndev); if (!in_dev) { np_err(np, "no IP address for %s, aborting\n", - egress_dev(np, buf)); + egress_dev(np, buf, sizeof(buf))); return -EDESTADDRREQ; } ifa = rtnl_dereference(in_dev->ifa_list); if (!ifa) { np_err(np, "no IP address for %s, aborting\n", - egress_dev(np, buf)); + egress_dev(np, buf, sizeof(buf))); return -EDESTADDRREQ; } @@ -719,7 +721,8 @@ int netpoll_setup(struct netpoll *np) ndev = dev_getbyhwaddr(net, ARPHRD_ETHER, np->dev_mac); if (!ndev) { - np_err(np, "%s doesn't exist, aborting\n", egress_dev(np, buf)); + np_err(np, "%s doesn't exist, aborting\n", + egress_dev(np, buf, sizeof(buf))); err = -ENODEV; goto unlock; } @@ -727,14 +730,14 @@ int netpoll_setup(struct netpoll *np) if (netdev_master_upper_dev_get(ndev)) { np_err(np, "%s is a slave device, aborting\n", - egress_dev(np, buf)); + egress_dev(np, buf, sizeof(buf))); err = -EBUSY; goto put; } if (!netif_running(ndev)) { np_info(np, "device %s not up yet, forcing it\n", - egress_dev(np, buf)); + egress_dev(np, buf, sizeof(buf))); err = dev_open(ndev, NULL); if (err) {