From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f180.google.com (mail-pg1-f180.google.com [209.85.215.180]) (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 C783D260566 for ; Sun, 15 Feb 2026 14:28:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771165700; cv=none; b=doDs0LCoZRaaTAeYtBTEO8b72e8qZwlhaK8aOMzvGMSW4HnlKijF2q8PHCln0uQqdfT/kXTOaTg2jeHrKy+9mlE19hIhMRVy5TRPTMoKMKQqYKK0arMFrRPDoLHfcI9CqoZc3rHrNGhYvP+Nm8RPC3IBQ4y5J2M6J8VSdsJRZaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771165700; c=relaxed/simple; bh=FoWGJBGz/L5d8YND8/UduWTl6mz34JwH1VU273nvY4Q=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=p2JdTGaBMj9fv94tUUTb7K68HPa5ukYw0PK1O3486dnG4O8YhZr0PiUG9I54G3xHqb9YdUyPSjXhW+LPmeQrkbj+EKkhpzzYXWrj4z3DV/CE8jUDgZsas48dX0H/Euqxc5bEERBtn8MHjIL/ovFPrfIbVZRdiJORxEeCLt8BbCQ= 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=NoL+SrJI; arc=none smtp.client-ip=209.85.215.180 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="NoL+SrJI" Received: by mail-pg1-f180.google.com with SMTP id 41be03b00d2f7-c636487ccaeso857130a12.1 for ; Sun, 15 Feb 2026 06:28:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1771165698; x=1771770498; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=sWjl7HPGBvhnIjt2NDHXlQWtF6bLS3V03uS6JDUla/0=; b=NoL+SrJIhPa49dfMlFjnJe33V017RStJ9+UCT8hF7reIcLt2dVlZw9zCC+BU7Cio9h 9QCesoBLsQbr2ozCHYK2Sh2HcqxvxBi4fQU47sYmCTgPr2Mjemy0tVg3UGOMhK2FRkOk 82SPLpqDEfk6Ug3E8OYInAXtSAXsTj62Xo9LBH7iX3IwVa19mxZRP6dkBZwCQ8RCAaCG Rs/yLoWhtacA1icRHhgioQlfLOsf+r4BNWfnijuaPXikiciZWxmESmJzo5Qg+JgncUT7 g2XZIRj9MA+lF6gsbZLttFF0RmxycHrmbdVMco6eiv1ZEYRdPZeLb8mQkA3gtVMu0xXj PJtw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771165698; x=1771770498; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=sWjl7HPGBvhnIjt2NDHXlQWtF6bLS3V03uS6JDUla/0=; b=nJh5MqV09eDuMmVKPwdJP3w0EH+Z1UtvX0mhMTDVErzd5Cpph6zh8Jgdj7RhFfwftA ZE3QAO6eK4RkmRIeQMwMT1ZtFIFveKf8MteNPjs4gqyI7qjgNURfaSdEkfHtDfR3pI3p 2GL8oiG05sOsEn6rgOTxwLHEutF5whAu3ZUI8e0SMgEDketH9+Ecv5gprReWrxfkzi// 5Yg6MIN4JqoFQsWN4YPbDzfYCEVkv/GgUeNeHSZUPFYLgoS7wNbMyyzPxzj8LxA8r0bF nU2rbSYgksbhKqJastSZUT0ff9JYlgjZUiyEvow/EW4yGytOdSpCuaqT87mXZdHKiT8q Ahhw== X-Forwarded-Encrypted: i=1; AJvYcCX6Gl6eZE1qOC1ei75mHFcjs6lobvDNs5KEG0Dzd5/fGR0kGR7QubM3XOJ8gQQy5iqdbNlrtoyOW273H8g=@vger.kernel.org X-Gm-Message-State: AOJu0YxHNqeK5i1bGoUTwfpNX/vzAs7LVX16Fy6jO/WxAj13R+8Ru24o OJ2C8VvXm+yRuLWZICKqJa1Khf6I4wM4tLa55cxfsbjJ9cqyM7sizArT X-Gm-Gg: AZuq6aL+6b4d+u4sajsVZmucxuTLNIrcd39nlzOQVSHQSBh37mlAqKQ2PDrq7kVc57E E/Ouhr2yhzi5xzK6StZvNt+vbcI3dlLoxJchHKT6c5MRMlwBpnUtZJY1VwFd+36S/w3Wat00S0/ l4ltYtXxmCGbL5j6uYv1BSvSPC0xNkgtq6xk4YhKN2Ual2oVcCIc0KKJuxiMYAqV2z8goLwK49G v9YqlmSq1T6Epq5ylNbdA4+qc2XCp93ew3eZSxB+EpyQnR5xCG7+jZcTbfiprbN7GwS+7LwQZdR sXWUg2EmVBr1luuVvwkQ3Ejy5s8dytqNN1uBcWHPVKyMzD3YDVf+3NN2Q4Z6SP5jlSNJbhmRMAe nDNVIiAlAEZS1b7SB99Zf1V08XCC1GOnfmoKJHCQaF89nh7xdE8zxP3A1XPOIEVcqwzUbg2fKfp q2nAWFY8FQGk5zFI8PrDhxliHSfVAVQYJYccWZAyw/Qst+q0KH8yKwTqCN X-Received: by 2002:a17:902:ce89:b0:2a9:ebc0:cce2 with SMTP id d9443c01a7336-2ab50558599mr73616455ad.18.1771165697939; Sun, 15 Feb 2026 06:28:17 -0800 (PST) Received: from speedy3.lan ([116.197.216.237]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ad1ace5bd1sm45617415ad.90.2026.02.15.06.28.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Feb 2026 06:28:17 -0800 (PST) From: "Marcel W. Wysocki" To: Richard Weinberger , Anton Ivanov , Johannes Berg Cc: linux-um@lists.infradead.org, linux-kernel@vger.kernel.org, "Marcel W . Wysocki" Subject: [PATCH 1/2] um: fix address-of CMSG_DATA() rvalue in stub Date: Sun, 15 Feb 2026 22:28:02 +0800 Message-ID: <20260215142803.1455757-1-maci.stgn@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The UML stub takes the address of CMSG_DATA(fd_msg): fd_map = (void *)&CMSG_DATA(fd_msg); CMSG_DATA() is specified by POSIX to return unsigned char *. Taking its address is semantically wrong -- the intent is to get a pointer to the control message data, which is exactly what CMSG_DATA() already returns. This happens to compile with glibc because glibc's primary CMSG_DATA definition accesses a flexible array member: #define CMSG_DATA(cmsg) ((cmsg)->__cmsg_data) An array lvalue can have its address taken, and &array yields the same address as array. However, glibc also has an alternative definition that uses pointer arithmetic (returning an rvalue), and musl's definition always uses pointer arithmetic: /* musl */ #define CMSG_DATA(cmsg) \ ((unsigned char *)(((struct cmsghdr *)(cmsg)) + 1)) Taking the address of an rvalue is a hard error in C, so the current code fails to compile with musl libc. Remove the erroneous & operator. The resulting code is correct regardless of the CMSG_DATA implementation -- it simply assigns the data pointer, which is what the subsequent code (fd_map[--num_fds]) expects. No functional change with glibc; fixes the build with musl. Signed-off-by: Marcel W. Wysocki --- arch/um/kernel/skas/stub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/um/kernel/skas/stub.c b/arch/um/kernel/skas/stub.c --- a/arch/um/kernel/skas/stub.c +++ b/arch/um/kernel/skas/stub.c @@ -146,7 +146,7 @@ /* Receive the FDs */ num_fds = 0; fd_msg = msghdr.msg_control; - fd_map = (void *)&CMSG_DATA(fd_msg); + fd_map = (void *)CMSG_DATA(fd_msg); if (res == iov.iov_len && msghdr.msg_controllen > sizeof(struct cmsghdr)) num_fds = (fd_msg->cmsg_len - CMSG_LEN(0)) / sizeof(int);