From: Jonathan Corbet <corbet@lwn.net>
To: cluster-devel.redhat.com
Subject: [Cluster-devel] [RFC PATCH 5/5] gfs2: Add xreaddir file operation and supporting functions
Date: Wed, 30 Jul 2014 09:57:09 -0400 [thread overview]
Message-ID: <20140730095709.62bade17@lwn.net> (raw)
In-Reply-To: <584806381.15003446.1406672757956.JavaMail.zimbra@redhat.com>
On Tue, 29 Jul 2014 18:25:57 -0400 (EDT)
Abhijith Das <adas@redhat.com> wrote:
> > > + if ((xc->xc_xattr_mask & XSTAT_XATTR_ALL) &&
> > > + lxd->xd_blob.xb_xattr_count) {
> >
> > How can that be right? lxd is __user, it doesn't seem right to be
> > dereferencing it directly...?
>
> Wouldn't the call to access_ok() at the start of the syscall take care of this? All the
> __user pointers point to areas within the user supplied buffer buf and overflow past the
> end of the buffer for the last lxd is checked for.
No, dereferencing user-space pointers in the kernel is never OK. What
if user space remapped that page after the access_ok() call? You need
to use copy_*_user() to get at user-space structures from the kernel.
jon
WARNING: multiple messages have this Message-ID (diff)
From: Jonathan Corbet <corbet@lwn.net>
To: Abhijith Das <adas@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
cluster-devel@redhat.com
Subject: Re: [RFC PATCH 5/5] gfs2: Add xreaddir file operation and supporting functions
Date: Wed, 30 Jul 2014 09:57:09 -0400 [thread overview]
Message-ID: <20140730095709.62bade17@lwn.net> (raw)
In-Reply-To: <584806381.15003446.1406672757956.JavaMail.zimbra@redhat.com>
On Tue, 29 Jul 2014 18:25:57 -0400 (EDT)
Abhijith Das <adas@redhat.com> wrote:
> > > + if ((xc->xc_xattr_mask & XSTAT_XATTR_ALL) &&
> > > + lxd->xd_blob.xb_xattr_count) {
> >
> > How can that be right? lxd is __user, it doesn't seem right to be
> > dereferencing it directly...?
>
> Wouldn't the call to access_ok() at the start of the syscall take care of this? All the
> __user pointers point to areas within the user supplied buffer buf and overflow past the
> end of the buffer for the last lxd is checked for.
No, dereferencing user-space pointers in the kernel is never OK. What
if user space remapped that page after the access_ok() call? You need
to use copy_*_user() to get at user-space structures from the kernel.
jon
next prev parent reply other threads:[~2014-07-30 13:57 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-25 17:38 [Cluster-devel] [RFC PATCH 0/5] xgetdents system call Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 17:38 ` [Cluster-devel] [RFC PATCH 1/5] fs: xstat system call VFS bits Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 18:17 ` [Cluster-devel] " Bob Peterson
2014-07-25 18:17 ` Bob Peterson
2014-07-25 17:38 ` [Cluster-devel] [RFC PATCH 2/5] fs: Add xgetdents system call and xreaddir file operation Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-29 8:20 ` [Cluster-devel] " Michael Kerrisk
2014-07-29 8:20 ` Michael Kerrisk
2014-07-29 8:20 ` Michael Kerrisk
2014-07-25 17:38 ` [Cluster-devel] [RFC PATCH 3/5] gfs2: Add a dynamic buffer backed by a vector of pages Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 18:42 ` [Cluster-devel] " Bob Peterson
2014-07-25 18:42 ` Bob Peterson
2014-07-25 17:38 ` [Cluster-devel] [RFC PATCH 4/5] gfs2: Add sort functionality with extra parameter Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-25 17:38 ` [Cluster-devel] [RFC PATCH 5/5] gfs2: Add xreaddir file operation and supporting functions Abhi Das
2014-07-25 17:38 ` Abhi Das
2014-07-29 18:58 ` [Cluster-devel] " Jonathan Corbet
2014-07-29 18:58 ` Jonathan Corbet
2014-07-29 22:25 ` [Cluster-devel] " Abhijith Das
2014-07-29 22:25 ` Abhijith Das
2014-07-30 9:06 ` [Cluster-devel] " Steven Whitehouse
2014-07-30 13:57 ` Jonathan Corbet [this message]
2014-07-30 13:57 ` Jonathan Corbet
2014-07-29 8:18 ` [Cluster-devel] [RFC PATCH 0/5] xgetdents system call Michael Kerrisk
2014-07-29 8:18 ` Michael Kerrisk
2014-07-29 8:18 ` Michael Kerrisk
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