Re: [PATCH net-next v7 03/10] bpf,landlock: Define an eBPF program type for a Landlock rule

[MickaÃl SalaÃn]

On 24/08/2017 04:28, Alexei Starovoitov wrote:
> On Mon, Aug 21, 2017 at 02:09:26AM +0200, MickaÃl SalaÃn wrote:
>> Add a new type of eBPF program used by Landlock rules.
>>
>> This new BPF program type will be registered with the Landlock LSM
>> initialization.
>>
>> Add an initial Landlock Kconfig.
>>
>> Signed-off-by: MickaÃl SalaÃn <mic@xxxxxxxxxxx>
>> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
>> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
>> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
>> Cc: James Morris <james.l.morris@xxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
>> ---
>>
>> Changes since v6:
>> * add 3 more sub-events: IOCTL, LOCK, FCNTL
>>   https://lkml.kernel.org/r/2fbc99a6-f190-f335-bd14-04bdeed35571@xxxxxxxxxxx
>> * rename LANDLOCK_VERSION to LANDLOCK_ABI to better reflect its purpose,
>>   and move it from landlock.h to common.h
>> * rename BPF_PROG_TYPE_LANDLOCK to BPF_PROG_TYPE_LANDLOCK_RULE: an eBPF
>>   program could be used for something else than a rule
>> * simplify struct landlock_context by removing the arch and syscall_nr fields
>> * remove all eBPF map functions call, remove ABILITY_WRITE
>> * refactor bpf_landlock_func_proto() (suggested by Kees Cook)
>> * constify pointers
>> * fix doc inclusion
>>
>> Changes since v5:
>> * rename file hooks.c to init.c
>> * fix spelling
>>
>> Changes since v4:
>> * merge a minimal (not enabled) LSM code and Kconfig in this commit
>>
>> Changes since v3:
>> * split commit
>> * revamp the landlock_context:
>>   * add arch, syscall_nr and syscall_cmd (ioctl, fcntlâ) to be able to
>>     cross-check action with the event type
>>   * replace args array with dedicated fields to ease the addition of new
>>     fields
>> ---
>>  include/linux/bpf_types.h      |  3 ++
>>  include/uapi/linux/bpf.h       | 97 +++++++++++++++++++++++++++++++++++++++++
>>  security/Kconfig               |  1 +
>>  security/Makefile              |  2 +
>>  security/landlock/Kconfig      | 18 ++++++++
>>  security/landlock/Makefile     |  3 ++
>>  security/landlock/common.h     | 21 +++++++++
>>  security/landlock/init.c       | 98 ++++++++++++++++++++++++++++++++++++++++++
>>  tools/include/uapi/linux/bpf.h | 97 +++++++++++++++++++++++++++++++++++++++++
>>  9 files changed, 340 insertions(+)
>>  create mode 100644 security/landlock/Kconfig
>>  create mode 100644 security/landlock/Makefile
>>  create mode 100644 security/landlock/common.h
>>  create mode 100644 security/landlock/init.c
>>
>> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
>> index 6f1a567667b8..8bac93970a47 100644
>> --- a/include/linux/bpf_types.h
>> +++ b/include/linux/bpf_types.h
>> @@ -18,6 +18,9 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_KPROBE, kprobe_prog_ops)
>>  BPF_PROG_TYPE(BPF_PROG_TYPE_TRACEPOINT, tracepoint_prog_ops)
>>  BPF_PROG_TYPE(BPF_PROG_TYPE_PERF_EVENT, perf_event_prog_ops)
>>  #endif
>> +#ifdef CONFIG_SECURITY_LANDLOCK
>> +BPF_PROG_TYPE(BPF_PROG_TYPE_LANDLOCK_RULE, bpf_landlock_ops)
>> +#endif
>>  
>>  BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
>>  BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 8541ab85e432..20da634da941 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -129,6 +129,7 @@ enum bpf_prog_type {
>>  	BPF_PROG_TYPE_LWT_XMIT,
>>  	BPF_PROG_TYPE_SOCK_OPS,
>>  	BPF_PROG_TYPE_SK_SKB,
>> +	BPF_PROG_TYPE_LANDLOCK_RULE,
>>  };
>>  
>>  enum bpf_attach_type {
>> @@ -879,4 +880,100 @@ enum {
>>  #define TCP_BPF_IW		1001	/* Set TCP initial congestion window */
>>  #define TCP_BPF_SNDCWND_CLAMP	1002	/* Set sndcwnd_clamp */
>>  
>> +/**
>> + * enum landlock_subtype_event - event occurring when an action is performed on
>> + * a particular kernel object
>> + *
>> + * An event is a policy decision point which exposes the same context type
>> + * (especially the same arg[0-9] field types) for each rule execution.
>> + *
>> + * @LANDLOCK_SUBTYPE_EVENT_UNSPEC: invalid value
>> + * @LANDLOCK_SUBTYPE_EVENT_FS: generic filesystem event
>> + * @LANDLOCK_SUBTYPE_EVENT_FS_IOCTL: custom IOCTL sub-event
>> + * @LANDLOCK_SUBTYPE_EVENT_FS_LOCK: custom LOCK sub-event
>> + * @LANDLOCK_SUBTYPE_EVENT_FS_FCNTL: custom FCNTL sub-event
>> + */
>> +enum landlock_subtype_event {
>> +	LANDLOCK_SUBTYPE_EVENT_UNSPEC,
>> +	LANDLOCK_SUBTYPE_EVENT_FS,
>> +	LANDLOCK_SUBTYPE_EVENT_FS_IOCTL,
>> +	LANDLOCK_SUBTYPE_EVENT_FS_LOCK,
>> +	LANDLOCK_SUBTYPE_EVENT_FS_FCNTL,
>> +};
>> +#define _LANDLOCK_SUBTYPE_EVENT_LAST LANDLOCK_SUBTYPE_EVENT_FS_FCNTL
>> +
>> +/**
>> + * DOC: landlock_subtype_ability
>> + *
>> + * eBPF context and functions allowed for a rule
>> + *
>> + * - LANDLOCK_SUBTYPE_ABILITY_DEBUG: allows to do debug actions (e.g. writing
>> + *   logs), which may be dangerous and should only be used for rule testing
>> + */
>> +#define LANDLOCK_SUBTYPE_ABILITY_DEBUG		(1ULL << 0)
>> +#define _LANDLOCK_SUBTYPE_ABILITY_NB		1
>> +#define _LANDLOCK_SUBTYPE_ABILITY_MASK		((1ULL << _LANDLOCK_SUBTYPE_ABILITY_NB) - 1)
> 
> can you move the last two macros out of uapi?
> There is really no need for the implementation details to
> leak into uapi.

Right, I'll move them.

> 
>> +
>> +/*
>> + * Future options for a Landlock rule (e.g. run even if a previous rule denied
>> + * an action).
>> + */
>> +#define _LANDLOCK_SUBTYPE_OPTION_NB		0
>> +#define _LANDLOCK_SUBTYPE_OPTION_MASK		((1ULL << _LANDLOCK_SUBTYPE_OPTION_NB) - 1)
> 
> same here
> 
>> +
>> +/*
>> + * Status visible in the @status field of a context (e.g. already called in
>> + * this syscall session, with same args...).
>> + *
>> + * The @status field exposed to a rule shall depend on the rule version.
>> + */
>> +#define _LANDLOCK_SUBTYPE_STATUS_NB		0
>> +#define _LANDLOCK_SUBTYPE_STATUS_MASK		((1ULL << _LANDLOCK_SUBTYPE_STATUS_NB) - 1)
> 
> and here
> 
>> +
>> +/**
>> + * DOC: landlock_action_fs
>> + *
>> + * - %LANDLOCK_ACTION_FS_EXEC: execute a file or walk through a directory
>> + * - %LANDLOCK_ACTION_FS_WRITE: modify a file or a directory view (which
>> + *   include mount actions)
>> + * - %LANDLOCK_ACTION_FS_READ: read a file or a directory
>> + * - %LANDLOCK_ACTION_FS_NEW: create a file or a directory
>> + * - %LANDLOCK_ACTION_FS_GET: open or receive a file
>> + * - %LANDLOCK_ACTION_FS_REMOVE: unlink a file or remove a directory
>> + *
>> + * Each of the following actions are specific to syscall multiplexers. Each of
>> + * them trigger a dedicated Landlock event where their command can be read.
>> + *
>> + * - %LANDLOCK_ACTION_FS_IOCTL: ioctl command
>> + * - %LANDLOCK_ACTION_FS_LOCK: flock or fcntl lock command
>> + * - %LANDLOCK_ACTION_FS_FCNTL: fcntl command
>> + */
>> +#define LANDLOCK_ACTION_FS_EXEC			(1ULL << 0)
>> +#define LANDLOCK_ACTION_FS_WRITE		(1ULL << 1)
>> +#define LANDLOCK_ACTION_FS_READ			(1ULL << 2)
>> +#define LANDLOCK_ACTION_FS_NEW			(1ULL << 3)
>> +#define LANDLOCK_ACTION_FS_GET			(1ULL << 4)
>> +#define LANDLOCK_ACTION_FS_REMOVE		(1ULL << 5)
>> +#define LANDLOCK_ACTION_FS_IOCTL		(1ULL << 6)
>> +#define LANDLOCK_ACTION_FS_LOCK			(1ULL << 7)
>> +#define LANDLOCK_ACTION_FS_FCNTL		(1ULL << 8)
>> +#define _LANDLOCK_ACTION_FS_NB			9
>> +#define _LANDLOCK_ACTION_FS_MASK		((1ULL << _LANDLOCK_ACTION_FS_NB) - 1)
> 
> and here
> 
>> +
>> +
>> +/**
>> + * struct landlock_context - context accessible to a Landlock rule
>> + *
>> + * @status: bitfield for future use (LANDLOCK_SUBTYPE_STATUS_*)
>> + * @event: event type (&enum landlock_subtype_event)
>> + * @arg1: event's first optional argument
>> + * @arg2: event's second optional argument
>> + */
>> +struct landlock_context {
>> +	__u64 status;
>> +	__u64 event;
>> +	__u64 arg1;
>> +	__u64 arg2;
>> +};
> 
> looking at all the uapi additions.. probably worth moving them
> into separate .h like we did with bpf_perf_event.h
> How about include/uapi/linux/landlock.h ?
> It can include bpf.h first thing and then the rest of
> landlock related bits.
> so all, but BPF_PROG_TYPE_LANDLOCK_RULE will go there.

Sounds good.


> 
>> +++ b/security/landlock/Kconfig
>> @@ -0,0 +1,18 @@
>> +config SECURITY_LANDLOCK
>> +	bool "Landlock sandbox support"
>> +	depends on SECURITY
>> +	depends on BPF_SYSCALL
>> +	depends on SECCOMP_FILTER
>> +	default y
> 
> all new features need to start with default n

OK

> 
>> +static inline const struct bpf_func_proto *bpf_landlock_func_proto(
>> +		enum bpf_func_id func_id,
>> +		const union bpf_prog_subtype *prog_subtype)
>> +{
>> +	/* generic functions */
>> +	if (prog_subtype->landlock_rule.ability &
>> +			LANDLOCK_SUBTYPE_ABILITY_DEBUG) {
>> +		switch (func_id) {
>> +		case BPF_FUNC_get_current_comm:
>> +			return &bpf_get_current_comm_proto;
>> +		case BPF_FUNC_get_current_pid_tgid:
>> +			return &bpf_get_current_pid_tgid_proto;
>> +		case BPF_FUNC_get_current_uid_gid:
>> +			return &bpf_get_current_uid_gid_proto;
> 
> why current_*() helpers are 'debug' only?

This helpers should not be needed for access control. It sounds like a
really bad idea to rely on a command name, a PID or even the UID,
especially for a kind of hierarchy-based access control like Landlock. I
want to avoid people from using these features except for debug
purposes. This could be changed in the future if there is a legitimate
use case of some of these features, though.

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