From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:39656 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758770AbdAJRsy (ORCPT ); Tue, 10 Jan 2017 12:48:54 -0500 Date: Tue, 10 Jan 2017 18:49:14 +0100 From: Greg KH To: Robin Murphy Cc: Jason@zx2c4.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] drivers: char: mem: Fix thinkos in kmem address checks Message-ID: <20170110174914.GA27165@kroah.com> References: <641a72e66f81d1244d8420074bc5def88d3929d4.1483529604.git.robin.murphy@arm.com> <1b8da4cd537f5dd91ff28450c78df893e0ff1622.1483632724.git.robin.murphy@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1b8da4cd537f5dd91ff28450c78df893e0ff1622.1483632724.git.robin.murphy@arm.com> Sender: stable-owner@vger.kernel.org List-ID: On Thu, Jan 05, 2017 at 05:15:01PM +0000, Robin Murphy wrote: > When borrowing the pfn_valid() check from mmap_kmem(), somebody managed > to get physical and virtual addresses spectacularly muddled up, such > that we've ended up with checks for one being the other. Whilst this > does indeed prevent out-of-bounds accesses crashing, on most systems > it also prevents the more desirable use-case of working at all ever. > > Check the *virtual* offset correctly for what it is. Furthermore, do > so in the right place - a read or write may span multiple pages, so a > single up-front check is insufficient. High memory accesses already > have a similar validity check just before the copy_to_user() call, so > just make the low memory path fully consistent with that. > > Reported-by: Jason A. Donenfeld > CC: stable@vger.kernel.org > Fixes: 148a1bc84398 ("drivers: char: mem: Check {read,write}_kmem() addresses") > Signed-off-by: Robin Murphy Jason, did this patch fix your issue? thanks, greg k-h > --- > > Third time lucky... And if there's some other problem with this one then > I guess we may as well just go ahead with Jason's revert, forget the whole > thing, and let 'cat /dev/kmem' go back to crashing on non-x86 :) > > Robin. > > drivers/char/mem.c | 10 ++++------ > 1 file changed, 4 insertions(+), 6 deletions(-) > > diff --git a/drivers/char/mem.c b/drivers/char/mem.c > index 5bb1985ec484..6d9cc2d39d22 100644 > --- a/drivers/char/mem.c > +++ b/drivers/char/mem.c > @@ -381,9 +381,6 @@ 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 -EIO; > - > read = 0; > if (p < (unsigned long) high_memory) { > low_count = count; > @@ -412,6 +409,8 @@ static ssize_t read_kmem(struct file *file, char __user *buf, > * by the kernel or data corruption may occur > */ > kbuf = xlate_dev_kmem_ptr((void *)p); > + if (!virt_addr_valid(kbuf)) > + return -ENXIO; > > if (copy_to_user(buf, kbuf, sz)) > return -EFAULT; > @@ -482,6 +481,8 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf, > * corruption may occur. > */ > ptr = xlate_dev_kmem_ptr((void *)p); > + if (!virt_addr_valid(ptr)) > + return -ENXIO; > > copied = copy_from_user(ptr, buf, sz); > if (copied) { > @@ -512,9 +513,6 @@ 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 -EIO; > - > if (p < (unsigned long) high_memory) { > unsigned long to_write = min_t(unsigned long, count, > (unsigned long)high_memory - p); > -- > 2.10.2.dirty