From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:37672 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755138AbeBOIca (ORCPT ); Thu, 15 Feb 2018 03:32:30 -0500 Subject: Patch "fs/proc/kcore.c: use probe_kernel_read() instead of memcpy()" has been added to the 4.14-stable tree To: heiko.carstens@de.ibm.com, akpm@linux-foundation.org, gregkh@linuxfoundation.org, jolsa@kernel.org, keescook@chromium.org, torvalds@linux-foundation.org, viro@ZenIV.linux.org.uk Cc: , From: Date: Thu, 15 Feb 2018 09:32:10 +0100 Message-ID: <151868353014112@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled fs/proc/kcore.c: use probe_kernel_read() instead of memcpy() to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: fs-proc-kcore.c-use-probe_kernel_read-instead-of-memcpy.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From d0290bc20d4739b7a900ae37eb5d4cc3be2b393f Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Tue, 6 Feb 2018 15:37:13 -0800 Subject: fs/proc/kcore.c: use probe_kernel_read() instead of memcpy() From: Heiko Carstens commit d0290bc20d4739b7a900ae37eb5d4cc3be2b393f upstream. Commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data") added a bounce buffer to avoid hardened usercopy checks. Copying to the bounce buffer was implemented with a simple memcpy() assuming that it is always valid to read from kernel memory iff the kern_addr_valid() check passed. A simple, but pointless, test case like "dd if=/proc/kcore of=/dev/null" now can easily crash the kernel, since the former execption handling on invalid kernel addresses now doesn't work anymore. Also adding a kern_addr_valid() implementation wouldn't help here. Most architectures simply return 1 here, while a couple implemented a page table walk to figure out if something is mapped at the address in question. With DEBUG_PAGEALLOC active mappings are established and removed all the time, so that relying on the result of kern_addr_valid() before executing the memcpy() also doesn't work. Therefore simply use probe_kernel_read() to copy to the bounce buffer. This also allows to simplify read_kcore(). At least on s390 this fixes the observed crashes and doesn't introduce warnings that were removed with df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data"), even though the generic probe_kernel_read() implementation uses uaccess functions. While looking into this I'm also wondering if kern_addr_valid() could be completely removed...(?) Link: http://lkml.kernel.org/r/20171202132739.99971-1-heiko.carstens@de.ibm.com Fixes: df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data") Fixes: f5509cc18daa ("mm: Hardened usercopy") Signed-off-by: Heiko Carstens Acked-by: Kees Cook Cc: Jiri Olsa Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/proc/kcore.c | 18 +++++------------- 1 file changed, 5 insertions(+), 13 deletions(-) --- a/fs/proc/kcore.c +++ b/fs/proc/kcore.c @@ -512,23 +512,15 @@ read_kcore(struct file *file, char __use return -EFAULT; } else { if (kern_addr_valid(start)) { - unsigned long n; - /* * Using bounce buffer to bypass the * hardened user copy kernel text checks. */ - memcpy(buf, (char *) start, tsz); - n = copy_to_user(buffer, buf, tsz); - /* - * We cannot distinguish between fault on source - * and fault on destination. When this happens - * we clear too and hope it will trigger the - * EFAULT again. - */ - if (n) { - if (clear_user(buffer + tsz - n, - n)) + if (probe_kernel_read(buf, (void *) start, tsz)) { + if (clear_user(buffer, tsz)) + return -EFAULT; + } else { + if (copy_to_user(buffer, buf, tsz)) return -EFAULT; } } else { Patches currently in stable-queue which might be from heiko.carstens@de.ibm.com are queue-4.14/fs-proc-kcore.c-use-probe_kernel_read-instead-of-memcpy.patch