From: Calvin Owens <calvinowens@fb.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Al Viro <viro@zeniv.linux.org.uk>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Peter Feiner <pfeiner@google.com>,
Grant Likely <grant.likely@secretlab.ca>,
Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
Pavel Emelyanov <xemul@openvz.org>
Subject: Re: [RFC][PATCH] procfs: Always expose /proc/<pid>/map_files/ and make it readable
Date: Thu, 22 Jan 2015 21:52:16 -0800 [thread overview]
Message-ID: <20150123055216.GB36613@mail.thefacebook.com> (raw)
In-Reply-To: <20150122212740.GA2286@node.dhcp.inet.fi>
On Thursday 01/22 at 23:27 +0200, Kirill A. Shutemov wrote:
> On Thu, Jan 22, 2015 at 01:00:25PM -0800, Calvin Owens wrote:
> > On Thursday 01/22 at 13:02 +0200, Kirill A. Shutemov wrote:
> > > On Wed, Jan 21, 2015 at 06:45:54PM -0800, Calvin Owens wrote:
> > > > Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
> > > > is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
> > > > is very useful for enumerating the files mapped into a process when
> > > > the more verbose information in /proc/<pid>/maps is not needed.
> > > >
> > > > This patch moves the folder out from behind CHECKPOINT_RESTORE, and
> > > > removes the CAP_SYS_ADMIN restrictions. To avoid exposing files to
> > > > processes for whom they may not be visible, a follow_link() stub is
> > > > added to the inode_operations struct attached to the symlinks that
> > > > prevent them from being followed without CAP_SYS_ADMIN.
> > > >
> > > > Signed-off-by: Calvin Owens <calvinowens@fb.com>
> > > > ---
> > > > fs/proc/base.c | 42 +++++++++++++++++++++++-------------------
> > > > 1 file changed, 23 insertions(+), 19 deletions(-)
> > > >
> > > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > > index 3f3d7ae..7d48003 100644
> > > > --- a/fs/proc/base.c
> > > > +++ b/fs/proc/base.c
> > > > @@ -1632,8 +1632,6 @@ end_instantiate:
> > > > return dir_emit(ctx, name, len, 1, DT_UNKNOWN);
> > > > }
> > > >
> > > > -#ifdef CONFIG_CHECKPOINT_RESTORE
> > > > -
> > > > /*
> > > > * dname_to_vma_addr - maps a dentry name into two unsigned longs
> > > > * which represent vma start and end addresses.
> > > > @@ -1660,11 +1658,6 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
> > > > if (flags & LOOKUP_RCU)
> > > > return -ECHILD;
> > > >
> > > > - if (!capable(CAP_SYS_ADMIN)) {
> > > > - status = -EPERM;
> > > > - goto out_notask;
> > > > - }
> > > > -
> > > > inode = dentry->d_inode;
> > > > task = get_proc_task(inode);
> > > > if (!task)
> > > > @@ -1753,6 +1746,28 @@ struct map_files_info {
> > > > unsigned char name[4*sizeof(long)+2]; /* max: %lx-%lx\0 */
> > > > };
> > > >
> > > > +/*
> > > > + * Allowing any user to follow the symlinks in /proc/<pid>/map_files/ could
> > > > + * allow processes to access files that should not be visible to them, so
> > > > + * restrict follow_link() to CAP_SYS_ADMIN for these files.
> > > > + */
> > > > +static void *proc_map_files_follow_link(struct dentry *d, struct nameidata *n)
> > > > +{
> > > > + if (!capable(CAP_SYS_ADMIN))
> > > > + return ERR_PTR(-EPERM);
> > > > +
> > > > + return proc_pid_follow_link(d, n);
> > > > +}
> > >
> > > I have thought a bit more about this and not sure it's reasonable to
> > > limit it to CAP_SYS_ADMIN. What scenario are we protecting from?
> > >
> > > Initially, I thought about something like this: privileged process opens a
> > > file, map part of it, closes the file and drop privileges with hope to
> > > limit further access to mapped window of the file. But I don't see what
> > > would stop the unprivileged process from accessing rest of the file using
> > > mremap(2). And if a process can do this, anybody who can ptrace(2) the
> > > process can do this.
> > >
> > > Am I missing something?
> >
> > The specific case I was thinking of is a process in a chroot with a
> > mounted /proc inside of it: if a process inside the chroot has the same
> > UID as a process outside of it, the chroot'ed process could follow the
> > symlinks in map_files/ and poke files it can't actually see, right?
>
> It depends on how you define "poke". If you mean touch content of the
> file, then, well, you can do it now. You cannot do anything which requires
> file descriptor -- open(), ftrancate(), etc.
Ah okay, I didn't realize you couldn't get the file descriptor. I wrote
a quick test case, you get -EACCES on open() in my chroot scenario.
I'll resend without the CAP_SYS_ADMIN check.
Thanks,
Calvin
next prev parent reply other threads:[~2015-01-23 5:52 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-14 0:20 [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files Calvin Owens
2015-01-14 0:23 ` Calvin Owens
2015-01-14 14:13 ` Rasmus Villemoes
2015-01-14 14:37 ` Siddhesh Poyarekar
2015-01-14 14:53 ` Rasmus Villemoes
2015-01-14 21:03 ` Calvin Owens
2015-01-14 22:45 ` Andrew Morton
2015-01-14 23:51 ` Rasmus Villemoes
2015-01-16 1:15 ` Andrew Morton
2015-01-16 11:00 ` Kirill A. Shutemov
2015-01-14 15:25 ` Kirill A. Shutemov
2015-01-14 15:33 ` Cyrill Gorcunov
2015-01-14 20:46 ` Calvin Owens
2015-01-14 21:16 ` Cyrill Gorcunov
2015-01-22 2:45 ` [RFC][PATCH] procfs: Always expose /proc/<pid>/map_files/ and make it readable Calvin Owens
2015-01-22 7:16 ` Cyrill Gorcunov
2015-01-22 11:02 ` Kirill A. Shutemov
2015-01-22 21:00 ` Calvin Owens
2015-01-22 21:27 ` Kirill A. Shutemov
2015-01-23 5:52 ` Calvin Owens [this message]
2015-01-24 3:15 ` [RFC][PATCH v2] " Calvin Owens
2015-01-26 12:47 ` Kirill A. Shutemov
2015-01-26 21:00 ` Cyrill Gorcunov
2015-01-26 23:43 ` Andrew Morton
2015-01-27 0:15 ` Kees Cook
2015-01-27 7:37 ` Cyrill Gorcunov
2015-01-27 19:53 ` Kees Cook
2015-01-27 21:35 ` Cyrill Gorcunov
2015-01-27 21:46 ` Pavel Emelyanov
2015-01-27 0:19 ` Kirill A. Shutemov
2015-01-27 6:46 ` Cyrill Gorcunov
2015-01-27 6:50 ` Andrew Morton
2015-01-27 7:23 ` Cyrill Gorcunov
2015-01-28 4:38 ` Calvin Owens
2015-01-30 1:30 ` Kees Cook
2015-01-31 1:58 ` Calvin Owens
2015-02-02 14:01 ` Austin S Hemmelgarn
2015-02-04 3:53 ` Calvin Owens
2015-02-02 20:16 ` Andy Lutomirski
2015-02-04 3:28 ` Calvin Owens
2015-02-12 2:29 ` [RFC][PATCH v3] " Calvin Owens
2015-02-12 7:45 ` Cyrill Gorcunov
2015-02-14 20:40 ` [RFC][PATCH v4] " Calvin Owens
2015-03-10 22:17 ` Cyrill Gorcunov
2015-04-28 22:23 ` Calvin Owens
2015-04-29 7:32 ` Cyrill Gorcunov
2015-05-19 3:10 ` [PATCH v5] " Calvin Owens
2015-05-19 3:29 ` Joe Perches
2015-05-19 18:04 ` Andy Lutomirski
2015-05-21 1:52 ` Calvin Owens
2015-05-21 2:10 ` Andy Lutomirski
2015-06-09 3:39 ` [PATCH v6] " Calvin Owens
2015-06-09 17:27 ` Kees Cook
2015-06-09 17:47 ` Andy Lutomirski
2015-06-09 18:15 ` Cyrill Gorcunov
2015-06-09 21:13 ` Andrew Morton
2015-06-10 1:39 ` Calvin Owens
2015-06-10 20:58 ` Andrew Morton
2015-06-11 11:10 ` Alexey Dobriyan
2015-06-11 18:49 ` Andrew Morton
2015-06-12 9:55 ` Alexey Dobriyan
2015-06-19 2:32 ` [PATCH v7] " Calvin Owens
2015-07-15 22:21 ` Andrew Morton
2015-07-15 23:39 ` Calvin Owens
2015-02-14 20:44 ` [PATCH] procfs: Return -ESRCH on /proc/N/fd/* when PID N doesn't exist Calvin Owens
2015-01-14 22:40 ` [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files Kirill A. Shutemov
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