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From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Howells <dhowells@redhat.com>
Cc: Andrew Lutomirski <luto@kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Linux API <linux-api@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jann Horn <jannh@google.com>
Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]
Date: Thu, 12 Jul 2018 08:50:46 -0700	[thread overview]
Message-ID: <CA+55aFx+xm333ZZ7d2Z39QuhDu=0XM6nTMChbHvWQOXNk32yxw@mail.gmail.com> (raw)
In-Reply-To: <7002.1531407244@warthog.procyon.org.uk>

On Thu, Jul 12, 2018 at 7:54 AM David Howells <dhowells@redhat.com> wrote:
>
> I think we *have* to open the source files/devices with the creds of whoever
> called fsopen() or fspick() - that way you can't upgrade your privs by passing
> your context fd to a suid program.  To enforce this, I think it's simplest for
> fscontext_write() to call override_creds() right after taking the uapi_mutex
> and then call revert_creds() right before dropping the mutex.

No.

Don't play games with override_creds. It's wrong.

You have to use file->f_creds - no games, no garbage.

But "write()" simply is *NOT* a good "command" interface. If you want
to send a command, use an ioctl or a system call.

Because it's not just about credentials. It's not just about fooling a
suid app into writing an error message to a descriptor you wrote. It's
also about things like "splice()", which can write to your target
using a kernel buffer, and thus trick you into doing a command while
we have the context set to kernel addresses.

Are we trying to get away from that issue? Yes. But it's just another
example of why "write()" IS NOT TO BE USED FOR COMMANDS.

Only use write() for data.

That's final. We're not adding yet another clueless fuck-up of an
interface just because people cannot understand this very simple rule:
"write()" is for data, not for commands.

No more excuses.

                 Linus

  reply	other threads:[~2018-07-12 15:51 UTC|newest]

Thread overview: 113+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-10 22:41 [PATCH 00/32] VFS: Introduce filesystem context [ver #9] David Howells
2018-07-10 22:41 ` [PATCH 01/32] vfs: syscall: Add open_tree(2) to reference or clone a mount " David Howells
2018-07-10 22:41 ` [PATCH 02/32] vfs: syscall: Add move_mount(2) to move mounts around " David Howells
2018-07-10 22:41 ` [PATCH 03/32] teach move_mount(2) to work with OPEN_TREE_CLONE " David Howells
2018-07-10 22:41 ` [PATCH 04/32] vfs: Suppress MS_* flag defs within the kernel unless explicitly enabled " David Howells
2018-07-10 22:42 ` [PATCH 05/32] vfs: Introduce the basic header for the new mount API's filesystem context " David Howells
2018-07-10 22:42 ` [PATCH 06/32] vfs: Add LSM hooks for the new mount API " David Howells
2018-07-10 22:42 ` [PATCH 07/32] selinux: Implement the new mount API LSM hooks " David Howells
2018-07-11 14:08   ` Stephen Smalley
2018-07-10 22:42 ` [PATCH 08/32] smack: Implement filesystem context security " David Howells
2018-07-10 23:13   ` Casey Schaufler
2018-07-10 23:19   ` David Howells
2018-07-10 23:28     ` Casey Schaufler
2018-07-10 22:42 ` [PATCH 09/32] apparmor: Implement security hooks for the new mount API " David Howells
2018-07-10 22:42 ` [PATCH 10/32] tomoyo: " David Howells
2018-07-10 23:34   ` Tetsuo Handa
2018-07-10 22:42 ` [PATCH 11/32] vfs: Require specification of size of mount data for internal mounts " David Howells
2018-07-10 22:51   ` Linus Torvalds
2018-07-10 22:42 ` [PATCH 12/32] vfs: Separate changing mount flags full remount " David Howells
2018-07-10 22:42 ` [PATCH 13/32] vfs: Implement a filesystem superblock creation/configuration context " David Howells
2018-07-10 22:43 ` [PATCH 14/32] vfs: Remove unused code after filesystem context changes " David Howells
2018-07-10 22:43 ` [PATCH 15/32] procfs: Move proc_fill_super() to fs/proc/root.c " David Howells
2018-07-10 22:43 ` [PATCH 16/32] proc: Add fs_context support to procfs " David Howells
2018-07-10 22:43 ` [PATCH 17/32] ipc: Convert mqueue fs to fs_context " David Howells
2018-07-10 22:43 ` [PATCH 18/32] cpuset: Use " David Howells
2018-07-10 22:43 ` [PATCH 19/32] kernfs, sysfs, cgroup, intel_rdt: Support " David Howells
2018-07-10 22:43 ` [PATCH 20/32] hugetlbfs: Convert to " David Howells
2018-07-10 22:43 ` [PATCH 21/32] vfs: Remove kern_mount_data() " David Howells
2018-07-10 22:43 ` [PATCH 22/32] vfs: Provide documentation for new mount API " David Howells
2018-07-13  1:37   ` Randy Dunlap
2018-07-13  9:45   ` David Howells
2018-07-10 22:44 ` [PATCH 23/32] Make anon_inodes unconditional " David Howells
2018-07-10 22:44 ` [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation " David Howells
2018-07-10 23:59   ` Andy Lutomirski
2018-07-11  1:05     ` Linus Torvalds
2018-07-11  1:15       ` Al Viro
2018-07-11  1:33         ` Andy Lutomirski
2018-07-11  1:48         ` Linus Torvalds
2018-07-11  8:43         ` David Howells
2018-07-11  1:14     ` Jann Horn
2018-07-11  1:16       ` Al Viro
2018-07-11  8:42     ` David Howells
2018-07-11 16:03       ` Linus Torvalds
2018-07-11  7:22   ` David Howells
2018-07-11 16:38     ` Eric Biggers
2018-07-11 17:06     ` Andy Lutomirski
2018-07-12 14:54     ` David Howells
2018-07-12 15:50       ` Linus Torvalds [this message]
2018-07-12 16:00         ` Al Viro
2018-07-12 16:07           ` Linus Torvalds
2018-07-12 16:31             ` Al Viro
2018-07-12 16:39               ` Linus Torvalds
2018-07-12 17:14                 ` Linus Torvalds
2018-07-12 17:44                   ` Al Viro
2018-07-12 17:54                     ` Linus Torvalds
2018-07-12 17:52                 ` Al Viro
2018-07-12 16:23       ` Andy Lutomirski
2018-07-12 16:31         ` Linus Torvalds
2018-07-12 16:41         ` Al Viro
2018-07-12 16:58         ` Al Viro
2018-07-12 17:54           ` Andy Lutomirski
2018-07-12 20:23       ` David Howells
2018-07-12 20:25         ` Andy Lutomirski
2018-07-12 20:34         ` Linus Torvalds
2018-07-12 20:36           ` Linus Torvalds
2018-07-12 21:26         ` David Howells
2018-07-12 21:40           ` Linus Torvalds
2018-07-12 22:32           ` Theodore Y. Ts'o
2018-07-12 22:54           ` David Howells
2018-07-12 23:21             ` Andy Lutomirski
2018-07-12 23:23             ` Jann Horn
2018-07-12 23:33               ` Jann Horn
2018-07-12 23:35             ` David Howells
2018-07-12 23:50               ` Andy Lutomirski
2018-07-13  0:03               ` David Howells
2018-07-13  0:24                 ` Andy Lutomirski
2018-07-13  7:30                 ` David Howells
2018-07-19  1:30                   ` Eric W. Biederman
2018-07-13  2:35             ` Theodore Y. Ts'o
2018-07-12 21:00       ` David Howells
2018-07-12 21:29         ` Linus Torvalds
2018-07-13 13:27         ` David Howells
2018-07-13 15:01           ` Andy Lutomirski
2018-07-13 15:40           ` David Howells
2018-07-13 17:14             ` Andy Lutomirski
2018-07-17  9:40           ` David Howells
2018-07-11 15:51   ` Jonathan Corbet
2018-07-11 16:18   ` David Howells
2018-07-12 17:15   ` Greg KH
2018-07-12 17:20     ` Al Viro
2018-07-12 18:03       ` Greg KH
2018-07-12 18:30         ` Andy Lutomirski
2018-07-12 18:34           ` Al Viro
2018-07-12 18:35             ` Al Viro
2018-07-12 19:08           ` Greg KH
2018-07-10 22:44 ` [PATCH 25/32] vfs: syscall: Add fsmount() to create a mount for a superblock " David Howells
2018-07-10 22:44 ` [PATCH 26/32] vfs: syscall: Add fspick() to select a superblock for reconfiguration " David Howells
2018-07-10 22:44 ` [PATCH 27/32] vfs: Implement logging through fs_context " David Howells
2018-07-10 22:44 ` [PATCH 28/32] vfs: Add some logging to the core users of the fs_context log " David Howells
2018-07-10 22:44 ` [PATCH 29/32] afs: Add fs_context support " David Howells
2018-07-10 22:44 ` [PATCH 30/32] afs: Use fs_context to pass parameters over automount " David Howells
2018-07-10 22:44 ` [PATCH 31/32] vfs: syscall: Add fsinfo() to query filesystem information " David Howells
2018-07-10 22:45 ` [PATCH 32/32] afs: Add fsinfo support " David Howells
2018-07-10 22:52 ` [MANPAGE PATCH] Add manpages for move_mount(2) and open_tree(2) David Howells
2019-10-09  9:51   ` Michael Kerrisk (man-pages)
2018-07-10 22:54 ` [MANPAGE PATCH] Add manpage for fsopen(2), fspick(2) and fsmount(2) David Howells
2019-10-09  9:52   ` Michael Kerrisk (man-pages)
2018-07-10 22:55 ` [MANPAGE PATCH] Add manpage for fsinfo(2) David Howells
2019-10-09  9:52   ` Michael Kerrisk (man-pages)
2019-10-09 12:02   ` David Howells
2018-07-10 23:01 ` [PATCH 00/32] VFS: Introduce filesystem context [ver #9] Linus Torvalds
2018-07-12  0:46 ` David Howells
2018-07-18 21:29 ` Getting rid of the usage of write() -- was " David Howells

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