Re: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[James Morris <jmorris@namei.org>]

On Thu, 4 Jul 2019, Tetsuo Handa wrote:

> Hello.
> 
> Since it seems that Al has no comments, I'd like to send this patch to
> linux-next.git . What should I do? Do I need to set up a git tree?

Yes, you can create one at github or similar.


> 
> On 2019/06/22 13:45, Tetsuo Handa wrote:
> > From c63c4074300921d6d1c33c3b8dc9c84ebfededf5 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Date: Sat, 22 Jun 2019 13:14:26 +0900
> > Subject: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.
> > 
> > syzbot is reporting that use of SOCKET_I()->sk from open() can result in
> > use after free problem [1], for socket's inode is still reachable via
> > /proc/pid/fd/n despite destruction of SOCKET_I()->sk already completed.
> > 
> > But there is no point with calling security_file_open() on sockets
> > because open("/proc/pid/fd/n", !O_PATH) on sockets fails with -ENXIO.
> > 
> > There is some point with calling security_inode_getattr() on sockets
> > because stat("/proc/pid/fd/n") and fstat(open("/proc/pid/fd/n", O_PATH))
> > are valid. If we want to access "struct sock"->sk_{family,type,protocol}
> > fields, we will need to use security_socket_post_create() hook and
> > security_inode_free() hook in order to remember these fields because
> > security_sk_free() hook is called before the inode is destructed. But
> > since information which can be protected by checking
> > security_inode_getattr() on sockets is trivial, let's not be bothered by
> > "struct inode"->i_security management.
> > 
> > There is point with calling security_file_ioctl() on sockets. Since
> > ioctl(open("/proc/pid/fd/n", O_PATH)) is invalid, security_file_ioctl()
> > on sockets should remain safe.
> > 
> > [1] https://syzkaller.appspot.com/bug?id=73d590010454403d55164cca23bd0565b1eb3b74
> > 
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Reported-by: syzbot <syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com>
> > ---
> >  security/tomoyo/tomoyo.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
> > index 716c92e..8ea3f5d 100644
> > --- a/security/tomoyo/tomoyo.c
> > +++ b/security/tomoyo/tomoyo.c
> > @@ -126,6 +126,9 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
> >   */
> >  static int tomoyo_inode_getattr(const struct path *path)
> >  {
> > +	/* It is not safe to call tomoyo_get_socket_name(). */
> > +	if (S_ISSOCK(d_inode(path->dentry)->i_mode))
> > +		return 0;
> >  	return tomoyo_path_perm(TOMOYO_TYPE_GETATTR, path, NULL);
> >  }
> >  
> > @@ -316,6 +319,9 @@ static int tomoyo_file_open(struct file *f)
> >  	/* Don't check read permission here if called from do_execve(). */
> >  	if (current->in_execve)
> >  		return 0;
> > +	/* Sockets can't be opened by open(). */
> > +	if (S_ISSOCK(file_inode(f)->i_mode))
> > +		return 0;
> >  	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
> >  					    f->f_flags);
> >  }
> > 
> 

-- 
James Morris
<jmorris@namei.org>