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[209.132.180.67]) by mx.google.com with ESMTP id i6si964562oor.75.2020.04.01.09.49.00; Wed, 01 Apr 2020 09:49:13 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=pL+ObCtx; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732728AbgDAQry (ORCPT + 99 others); Wed, 1 Apr 2020 12:47:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:49722 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390092AbgDAQrt (ORCPT ); Wed, 1 Apr 2020 12:47:49 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 81835206E9; Wed, 1 Apr 2020 16:47:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585759669; bh=hWOZrHvnYSAf5XeSIOQqTauluJyu1ePX9xjyJ1biX1c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pL+ObCtxEWnuo4pWpm0fBzIbpDUV1lUnnN4zrdg0Tn8KinxJDWRKkWaJb38FOip7u qzGwv7kR5n8DcwwbbJlxOz4HuRqMRwSVEveNVzQcw4KqrfioG+htQPRiCgavInUKVU Fa8OrL5dbagv1ZvoqYBgf+81pTxnLboR4lfyx29Y= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+fcab69d1ada3e8d6f06b@syzkaller.appspotmail.com, Alexander Potapenko , Eric Biggers , Kees Cook Subject: [PATCH 4.14 125/148] libfs: fix infoleak in simple_attr_read() Date: Wed, 1 Apr 2020 18:18:37 +0200 Message-Id: <20200401161604.401620995@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200401161552.245876366@linuxfoundation.org> References: <20200401161552.245876366@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Biggers commit a65cab7d7f05c2061a3e2490257d3086ff3202c6 upstream. Reading from a debugfs file at a nonzero position, without first reading at position 0, leaks uninitialized memory to userspace. It's a bit tricky to do this, since lseek() and pread() aren't allowed on these files, and write() doesn't update the position on them. But writing to them with splice() *does* update the position: #define _GNU_SOURCE 1 #include #include #include int main() { int pipes[2], fd, n, i; char buf[32]; pipe(pipes); write(pipes[1], "0", 1); fd = open("/sys/kernel/debug/fault_around_bytes", O_RDWR); splice(pipes[0], NULL, fd, NULL, 1, 0); n = read(fd, buf, sizeof(buf)); for (i = 0; i < n; i++) printf("%02x", buf[i]); printf("\n"); } Output: 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a30 Fix the infoleak by making simple_attr_read() always fill simple_attr::get_buf if it hasn't been filled yet. Reported-by: syzbot+fcab69d1ada3e8d6f06b@syzkaller.appspotmail.com Reported-by: Alexander Potapenko Fixes: acaefc25d21f ("[PATCH] libfs: add simple attribute files") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers Acked-by: Kees Cook Link: https://lore.kernel.org/r/20200308023849.988264-1-ebiggers@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/libfs.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/fs/libfs.c +++ b/fs/libfs.c @@ -802,7 +802,7 @@ int simple_attr_open(struct inode *inode { struct simple_attr *attr; - attr = kmalloc(sizeof(*attr), GFP_KERNEL); + attr = kzalloc(sizeof(*attr), GFP_KERNEL); if (!attr) return -ENOMEM; @@ -842,9 +842,11 @@ ssize_t simple_attr_read(struct file *fi if (ret) return ret; - if (*ppos) { /* continued read */ + if (*ppos && attr->get_buf[0]) { + /* continued read */ size = strlen(attr->get_buf); - } else { /* first read */ + } else { + /* first read */ u64 val; ret = attr->get(attr->data, &val); if (ret)