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From: "Mickaël Salaün" <mic@digikod.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Arnd Bergmann <arnd@arndb.de>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Daniel Mack <daniel@zonque.org>,
	David Drysdale <drysdale@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	James Morris <james.l.morris@oracle.com>,
	Kees Cook <keescook@chromium.org>, Paul Moore <pmoore@redhat.com>,
	Sargun Dhillon <sargun@sargun.me>,
	"Serge E . Hallyn" <serge@hallyn.com>, Tejun Heo <tj@kernel.org>,
	Will Drewry <wad@chromium.org>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-security-module@vger.kernel.org, netdev@vger.kernel.org,
	cgroups@vger.kernel.org
Subject: Re: [RFC v3 07/22] landlock: Handle file comparisons
Date: Thu, 15 Sep 2016 01:02:22 +0200
Message-ID: <57D9D6FE.4090708@digikod.net> (raw)
In-Reply-To: <20160914210649.GA57174@ast-mbp.thefacebook.com>

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On 14/09/2016 23:06, Alexei Starovoitov wrote:
> On Wed, Sep 14, 2016 at 09:24:00AM +0200, Mickaël Salaün wrote:
>> Add eBPF functions to compare file system access with a Landlock file
>> system handle:
>> * bpf_landlock_cmp_fs_prop_with_struct_file(prop, map, map_op, file)
>>   This function allows to compare the dentry, inode, device or mount
>>   point of the currently accessed file, with a reference handle.
>> * bpf_landlock_cmp_fs_beneath_with_struct_file(opt, map, map_op, file)
>>   This function allows an eBPF program to check if the current accessed
>>   file is the same or in the hierarchy of a reference handle.
>>
>> The goal of file system handle is to abstract kernel objects such as a
>> struct file or a struct inode. Userland can create this kind of handle
>> thanks to the BPF_MAP_UPDATE_ELEM command. The element is a struct
>> landlock_handle containing the handle type (e.g.
>> BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) and a file descriptor. This could
>> also be any descriptions able to match a struct file or a struct inode
>> (e.g. path or glob string).
>>
>> Changes since v2:
>> * add MNT_INTERNAL check to only add file handle from user-visible FS
>>   (e.g. no anonymous inode)
>> * replace struct file* with struct path* in map_landlock_handle
>> * add BPF protos
>> * fix bpf_landlock_cmp_fs_prop_with_struct_file()
>>
>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>> Cc: Alexei Starovoitov <ast@kernel.org>
>> Cc: Andy Lutomirski <luto@amacapital.net>
>> Cc: Daniel Borkmann <daniel@iogearbox.net>
>> Cc: David S. Miller <davem@davemloft.net>
>> Cc: James Morris <james.l.morris@oracle.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Serge E. Hallyn <serge@hallyn.com>
>> Link: https://lkml.kernel.org/r/CALCETrWwTiz3kZTkEgOW24-DvhQq6LftwEXh77FD2G5o71yD7g@mail.gmail.com
> 
> thanks for keeping the links to the previous discussion.
> Long term it should help, though I worry we already at the point
> where there are too many outstanding issues to resolve before we
> can proceed with reasonable code review.
> 
>> +/*
>> + * bpf_landlock_cmp_fs_prop_with_struct_file
>> + *
>> + * Cf. include/uapi/linux/bpf.h
>> + */
>> +static inline u64 bpf_landlock_cmp_fs_prop_with_struct_file(u64 r1_property,
>> +		u64 r2_map, u64 r3_map_op, u64 r4_file, u64 r5)
>> +{
>> +	u8 property = (u8) r1_property;
>> +	struct bpf_map *map = (struct bpf_map *) (unsigned long) r2_map;
>> +	enum bpf_map_array_op map_op = r3_map_op;
>> +	struct file *file = (struct file *) (unsigned long) r4_file;
> 
> please use just added BPF_CALL_ macros. They will help readability of the above.
> 
>> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
>> +	struct path *p1, *p2;
>> +	struct map_landlock_handle *handle;
>> +	int i;
>> +
>> +	/* ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS is an arraymap */
>> +	if (unlikely(!map)) {
>> +		WARN_ON(1);
>> +		return -EFAULT;
>> +	}
>> +	if (unlikely(!file))
>> +		return -ENOENT;
>> +	if (unlikely((property | _LANDLOCK_FLAG_FS_MASK) != _LANDLOCK_FLAG_FS_MASK))
>> +		return -EINVAL;
>> +
>> +	/* for now, only handle OP_OR */
>> +	switch (map_op) {
>> +	case BPF_MAP_ARRAY_OP_OR:
>> +		break;
>> +	case BPF_MAP_ARRAY_OP_UNSPEC:
>> +	case BPF_MAP_ARRAY_OP_AND:
>> +	case BPF_MAP_ARRAY_OP_XOR:
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +	p2 = &file->f_path;
>> +
>> +	synchronize_rcu();
> 
> that is completely broken.
> bpf programs are executing under rcu_lock.
> please enable CONFIG_PROVE_RCU and retest everything.

Thanks for the tip. I will fix this.

> 
> I would suggest for the next RFC to do minimal 7 patches up to this point
> with simple example that demonstrates the use case.
> I would avoid all unpriv stuff and all of seccomp for the next RFC as well,
> otherwise I don't think we can realistically make forward progress, since
> there are too many issues raised in the subsequent patches.

I hope we will find a common agreement about seccomp vs cgroup… I think
both approaches have their advantages, can be complementary and nicely
combined.

Unprivileged sandboxing is the main goal of Landlock. This should not be
a problem, even for privileged features, thanks to the new subtype/access.

> 
> The common part that is mergeable is prog's subtype extension to
> the verifier that can be used for better tracing and is the common
> piece of infra needed for both landlock and checmate LSMs
> (which must be one LSM anyway)

Agreed. With this RFC, the Checmate features (i.e. network helpers)
should be able to sit on top of Landlock.


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  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-14  7:23 [RFC v3 00/22] Landlock LSM: Unprivileged sandboxing Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 01/22] landlock: Add Kconfig Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 02/22] bpf: Move u64_to_ptr() to BPF headers and inline it Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 03/22] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles Mickaël Salaün
2016-09-14 18:51   ` Alexei Starovoitov
2016-09-14 23:22     ` Mickaël Salaün
2016-09-14 23:28       ` Alexei Starovoitov
2016-09-15 21:51         ` Mickaël Salaün
2016-10-03 23:53   ` Kees Cook
2016-10-05 22:02     ` Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 04/22] bpf: Set register type according to is_valid_access() Mickaël Salaün
2016-10-19 14:54   ` Thomas Graf
2016-10-19 15:10     ` Daniel Borkmann
2016-09-14  7:23 ` [RFC v3 05/22] bpf,landlock: Add eBPF program subtype and is_valid_subtype() verifier Mickaël Salaün
2016-10-19 15:01   ` Thomas Graf
2016-09-14  7:23 ` [RFC v3 06/22] landlock: Add LSM hooks Mickaël Salaün
2016-10-19 15:19   ` Thomas Graf
2016-10-19 22:42     ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 07/22] landlock: Handle file comparisons Mickaël Salaün
2016-09-14 19:07   ` Jann Horn
2016-09-14 22:39     ` Mickaël Salaün
2016-09-14 21:06   ` Alexei Starovoitov
2016-09-14 23:02     ` Mickaël Salaün [this message]
2016-09-14 23:24       ` Alexei Starovoitov
2016-09-15 21:25         ` Mickaël Salaün
2016-09-20  0:12           ` lsm naming dilemma. " Alexei Starovoitov
2016-09-20  1:10             ` Sargun Dhillon
2016-09-20 16:58               ` Mickaël Salaün
2016-10-03 23:30   ` Kees Cook
2016-09-14  7:24 ` [RFC v3 08/22] seccomp: Fix documentation for struct seccomp_filter Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 09/22] seccomp: Move struct seccomp_filter in seccomp.h Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 10/22] seccomp: Split put_seccomp_filter() with put_seccomp() Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 11/22] seccomp,landlock: Handle Landlock hooks per process hierarchy Mickaël Salaün
2016-09-14 18:43   ` Andy Lutomirski
2016-09-14 22:34     ` Mickaël Salaün
2016-10-03 23:52       ` Kees Cook
2016-10-05 21:05         ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 12/22] bpf: Cosmetic change for bpf_prog_attach() Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 13/22] bpf/cgroup: Replace struct bpf_prog with union bpf_object Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 14/22] bpf/cgroup: Make cgroup_bpf_update() return an error code Mickaël Salaün
2016-09-14 21:16   ` Alexei Starovoitov
2016-09-14  7:24 ` [RFC v3 15/22] bpf/cgroup: Move capability check Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per cgroup Mickaël Salaün
2016-10-03 23:43   ` Kees Cook
2016-10-05 20:58     ` Mickaël Salaün
2016-10-05 21:25       ` Kees Cook
2016-09-14  7:24 ` [RFC v3 17/22] cgroup: Add access check for cgroup_get_from_fd() Mickaël Salaün
2016-09-14 22:06   ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 18/22] cgroup,landlock: Add CGRP_NO_NEW_PRIVS to handle unprivileged hooks Mickaël Salaün
2016-09-14 18:27   ` Andy Lutomirski
2016-09-14 22:11     ` Mickaël Salaün
2016-09-15  1:25       ` Andy Lutomirski
2016-09-15  2:19         ` Alexei Starovoitov
2016-09-15  2:27           ` Andy Lutomirski
2016-09-15  4:00             ` Alexei Starovoitov
2016-09-15  4:08               ` Andy Lutomirski
2016-09-15  4:31                 ` Alexei Starovoitov
2016-09-15  4:38                   ` Andy Lutomirski
2016-09-15  4:48                     ` Alexei Starovoitov
2016-09-15 19:41                       ` Mickaël Salaün
2016-09-20  4:37                         ` Sargun Dhillon
2016-09-20 17:02                           ` Mickaël Salaün
2016-09-15 19:35         ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 19/22] landlock: Add interrupted origin Mickaël Salaün
2016-09-14 18:29   ` Andy Lutomirski
2016-09-14 22:14     ` Mickaël Salaün
2016-09-15  1:19       ` Andy Lutomirski
2016-10-03 23:46         ` Kees Cook
2016-10-05 21:01           ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 20/22] landlock: Add update and debug access flags Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 21/22] bpf,landlock: Add optional skb pointer in the Landlock context Mickaël Salaün
2016-09-14 21:20   ` Alexei Starovoitov
2016-09-14 22:46     ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 22/22] samples/landlock: Add sandbox example Mickaël Salaün
2016-09-14 21:24   ` Alexei Starovoitov
2016-09-14 14:36 ` [RFC v3 00/22] Landlock LSM: Unprivileged sandboxing David Laight

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