From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753538AbcEaMwx (ORCPT ); Tue, 31 May 2016 08:52:53 -0400 Received: from foss.arm.com ([217.140.101.70]:58808 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752542AbcEaMwv (ORCPT ); Tue, 31 May 2016 08:52:51 -0400 From: Robin Murphy To: arnd@arndb.de, gregkh@linuxfoundation.org Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, wangkefeng.wang@huawei.com Subject: [PATCH] drivers: char: mem: Check {read,write}_kmem() addresses Date: Tue, 31 May 2016 13:52:45 +0100 Message-Id: <5e293c103f0a86f512d71f17091a55e9746e711f.1464698496.git.robin.murphy@arm.com> X-Mailer: git-send-email 2.8.1.dirty Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Arriving at read_kmem() with an offset representing a bogus kernel address (e.g. 0 from a simple "cat /dev/kmem") leads to copy_to_user faulting on the kernel-space read. x86_64 happens to get away with this since the optimised implementation uses "rep movs*", thus the user write (which is allowed to fault) and the kernel read are the same instruction, the kernel-side fault falls into the userspace fixup handler and a chain of events transpires leading to returning the expected -EFAULT. On other architectures, though, the read is not covered by the fixup entry for the write, and we get a straightforward "Unable to hande kernel paging request..." dump. The more typical use-case of mmap_kmem() already validates the address with pfn_valid() as one might expect, so let's make that consistent across {read,write}_kem() too. Reported-by: Kefeng Wang Signed-off-by: Robin Murphy --- I'm not sure if this warrants going to stable or not, as it's really just making an existing failure case more graceful and less confusing. drivers/char/mem.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 71025c2f6bbb..64c766023b15 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -384,6 +384,9 @@ static ssize_t read_kmem(struct file *file, char __user *buf, char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */ int err = 0; + if (!pfn_valid(PFN_DOWN(p))) + return -EFAULT; + read = 0; if (p < (unsigned long) high_memory) { low_count = count; @@ -512,6 +515,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf, char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */ int err = 0; + if (!pfn_valid(PFN_DOWN(p))) + return -EFAULT; + if (p < (unsigned long) high_memory) { unsigned long to_write = min_t(unsigned long, count, (unsigned long)high_memory - p); -- 2.8.1.dirty