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From: Jann Horn <jann@thejh.net>
To: "Mickaël Salaün" <mic@digikod.net>
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: Wed, 14 Sep 2016 21:07:23 +0200
Message-ID: <20160914190723.GB5617@pc.thejh.net> (raw)
In-Reply-To: <20160914072415.26021-8-mic@digikod.net>


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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.
[...]
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 94256597eacd..edaab4c87292 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -603,6 +605,9 @@ static void landlock_put_handle(struct map_landlock_handle *handle)
>  	enum bpf_map_handle_type handle_type = handle->type;
>  
>  	switch (handle_type) {
> +	case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
> +		path_put(&handle->path);
> +		break;
>  	case BPF_MAP_HANDLE_TYPE_UNSPEC:
>  	default:
>  		WARN_ON(1);
[...]
> diff --git a/security/landlock/checker_fs.c b/security/landlock/checker_fs.c
> new file mode 100644
> index 000000000000..39eb85dc7d18
> --- /dev/null
> +++ b/security/landlock/checker_fs.c
[...]
> +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;
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
> +	struct path *p1, *p2;
> +	struct map_landlock_handle *handle;
> +	int i;

Please don't use int when iterating over an array, use size_t.


> +	/* for now, only handle OP_OR */

Is "OP_OR" an appropriate name for something that ANDs the success of
checks?


[...]
> +	synchronize_rcu();

Can you put a comment here that explains what's going on?


> +	for (i = 0; i < array->n_entries; i++) {
> +		bool result_dentry = !(property & LANDLOCK_FLAG_FS_DENTRY);
> +		bool result_inode = !(property & LANDLOCK_FLAG_FS_INODE);
> +		bool result_device = !(property & LANDLOCK_FLAG_FS_DEVICE);
> +		bool result_mount = !(property & LANDLOCK_FLAG_FS_MOUNT);
> +
> +		handle = (struct map_landlock_handle *)
> +				(array->value + array->elem_size * i);
> +
> +		if (handle->type != BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) {
> +			WARN_ON(1);
> +			return -EFAULT;
> +		}
> +		p1 = &handle->path;
> +
> +		if (!result_dentry && p1->dentry == p2->dentry)
> +			result_dentry = true;

Why is this safe? As far as I can tell, this is not in an RCU read-side
critical section (synchronize_rcu() was just called), and no lock has been
taken. What prevents someone from removing the arraymap entry while we're
looking at it? Am I missing something?


[...]
> +static inline u64 bpf_landlock_cmp_fs_beneath_with_struct_file(u64 r1_option,
> +		u64 r2_map, u64 r3_map_op, u64 r4_file, u64 r5)
> +{
> +	u8 option = (u8) r1_option;
> +	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;
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
> +	struct path *p1, *p2;
> +	struct map_landlock_handle *handle;
> +	int i;

As above, please use size_t.

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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 [this message]
2016-09-14 22:39     ` Mickaël Salaün
2016-09-14 21:06   ` Alexei Starovoitov
2016-09-14 23:02     ` Mickaël Salaün
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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