bpf: Implement cgroup sockaddr hooks for unix sockets

These hooks allows intercepting connect(), getsockname(),
getpeername(), sendmsg() and recvmsg() for unix sockets. The unix
socket hooks get write access to the address length because the
address length is not fixed when dealing with unix sockets and
needs to be modified when a unix socket address is modified by
the hook. Because abstract socket unix addresses start with a
NUL byte, we cannot recalculate the socket address in kernelspace
after running the hook by calculating the length of the unix socket
path using strlen().

These hooks can be used when users want to multiplex syscall to a
single unix socket to multiple different processes behind the scenes
by redirecting the connect() and other syscalls to process specific
sockets.

We do not implement support for intercepting bind() because when
using bind() with unix sockets with a pathname address, this creates
an inode in the filesystem which must be cleaned up. If we rewrite
the address, the user might try to clean up the wrong file, leaking
the socket in the filesystem where it is never cleaned up. Until we
figure out a solution for this (and a use case for intercepting bind()),
we opt to not allow rewriting the sockaddr in bind() calls.

We also implement recvmsg() support for connected streams so that
after a connect() that is modified by a sockaddr hook, any corresponding
recmvsg() on the connected socket can also be modified to make the
connected program think it is connected to the "intended" remote.

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Daan De Meyer <daan.j.demeyer@gmail.com>
Link: https://lore.kernel.org/r/20231011185113.140426-5-daan.j.demeyer@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

bpf: minimize number of allocated lsm slots per program

Previous patch adds 1:1 mapping between all 211 LSM hooks
and bpf_cgroup program array. Instead of reserving a slot per
possible hook, reserve 10 slots per cgroup for lsm programs.
Those slots are dynamically allocated on demand and reclaimed.

struct cgroup_bpf {
struct bpf_prog_array * effective[33]; /* 0 264 */
/* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */
struct hlist_head progs[33]; /* 264 264 */
/* --- cacheline 8 boundary (512 bytes) was 16 bytes ago --- */
u8 flags[33]; /* 528 33 */

/* XXX 7 bytes hole, try to pack */

struct list_head storages; /* 568 16 */
/* --- cacheline 9 boundary (576 bytes) was 8 bytes ago --- */
struct bpf_prog_array * inactive; /* 584 8 */
struct percpu_ref refcnt; /* 592 16 */
struct work_struct release_work; /* 608 72 */

/* size: 680, cachelines: 11, members: 7 */
/* sum members: 673, holes: 1, sum holes: 7 */
/* last cacheline: 40 bytes */
};

Reviewed-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220628174314.1216643-5-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf: per-cgroup lsm flavor

Allow attaching to lsm hooks in the cgroup context.

Attaching to per-cgroup LSM works exactly like attaching
to other per-cgroup hooks. New BPF_LSM_CGROUP is added
to trigger new mode; the actual lsm hook we attach to is
signaled via existing attach_btf_id.

For the hooks that have 'struct socket' or 'struct sock' as its first
argument, we use the cgroup associated with that socket. For the rest,
we use 'current' cgroup (this is all on default hierarchy == v2 only).
Note that for some hooks that work on 'struct sock' we still
take the cgroup from 'current' because some of them work on the socket
that hasn't been properly initialized yet.

Behind the scenes, we allocate a shim program that is attached
to the trampoline and runs cgroup effective BPF programs array.
This shim has some rudimentary ref counting and can be shared
between several programs attaching to the same lsm hook from
different cgroups.

Note that this patch bloats cgroup size because we add 211
cgroup_bpf_attach_type(s) for simplicity sake. This will be
addressed in the subsequent patch.

Also note that we only add non-sleepable flavor for now. To enable
sleepable use-cases, bpf_prog_run_array_cg has to grab trace rcu,
shim programs have to be freed via trace rcu, cgroup_bpf.effective
should be also trace-rcu-managed + maybe some other changes that
I'm not aware of.

Reviewed-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220628174314.1216643-4-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf: convert cgroup_bpf.progs to hlist

This lets us reclaim some space to be used by new cgroup lsm slots.

Before:
struct cgroup_bpf {
struct bpf_prog_array * effective[23]; /* 0 184 */
/* --- cacheline 2 boundary (128 bytes) was 56 bytes ago --- */
struct list_head progs[23]; /* 184 368 */
/* --- cacheline 8 boundary (512 bytes) was 40 bytes ago --- */
u32 flags[23]; /* 552 92 */

/* XXX 4 bytes hole, try to pack */

/* --- cacheline 10 boundary (640 bytes) was 8 bytes ago --- */
struct list_head storages; /* 648 16 */
struct bpf_prog_array * inactive; /* 664 8 */
struct percpu_ref refcnt; /* 672 16 */
struct work_struct release_work; /* 688 32 */

/* size: 720, cachelines: 12, members: 7 */
/* sum members: 716, holes: 1, sum holes: 4 */
/* last cacheline: 16 bytes */
};

After:
struct cgroup_bpf {
struct bpf_prog_array * effective[23]; /* 0 184 */
/* --- cacheline 2 boundary (128 bytes) was 56 bytes ago --- */
struct hlist_head progs[23]; /* 184 184 */
/* --- cacheline 5 boundary (320 bytes) was 48 bytes ago --- */
u8 flags[23]; /* 368 23 */

/* XXX 1 byte hole, try to pack */

/* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
struct list_head storages; /* 392 16 */
struct bpf_prog_array * inactive; /* 408 8 */
struct percpu_ref refcnt; /* 416 16 */
struct work_struct release_work; /* 432 72 */

/* size: 504, cachelines: 8, members: 7 */
/* sum members: 503, holes: 1, sum holes: 1 */
/* last cacheline: 56 bytes */
};

Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220628174314.1216643-3-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf: Remove the cgroup -> bpf header dependecy

Remove the dependency from cgroup-defs.h to bpf-cgroup.h and bpf.h.
This reduces the incremental build size of x86 allmodconfig after
bpf.h was touched from ~17k objects rebuilt to ~5k objects.
bpf.h is 2.2kLoC and is modified relatively often.

We need a new header with just the definition of struct cgroup_bpf
and enum cgroup_bpf_attach_type, this is akin to cgroup-defs.h.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/bpf/20211216025538.1649516-4-kuba@kernel.org