bpf: multi program support for cgroup+bpf

introduce BPF_F_ALLOW_MULTI flag that can be used to attach multiple
bpf programs to a cgroup.

The difference between three possible flags for BPF_PROG_ATTACH command:
- NONE(default): No further bpf programs allowed in the subtree.
- BPF_F_ALLOW_OVERRIDE: If a sub-cgroup installs some bpf program,
  the program in this cgroup yields to sub-cgroup program.
- BPF_F_ALLOW_MULTI: If a sub-cgroup installs some bpf program,
  that cgroup program gets run in addition to the program in this cgroup.

NONE and BPF_F_ALLOW_OVERRIDE existed before. This patch doesn't
change their behavior. It only clarifies the semantics in relation
to new flag.

Only one program is allowed to be attached to a cgroup with
NONE or BPF_F_ALLOW_OVERRIDE flag.
Multiple programs are allowed to be attached to a cgroup with
BPF_F_ALLOW_MULTI flag. They are executed in FIFO order
(those that were attached first, run first)
The programs of sub-cgroup are executed first, then programs of
this cgroup and then programs of parent cgroup.
All eligible programs are executed regardless of return code from
earlier programs.

To allow efficient execution of multiple programs attached to a cgroup
and to avoid penalizing cgroups without any programs attached
introduce 'struct bpf_prog_array' which is RCU protected array
of pointers to bpf programs.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
for cgroup bits
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 11 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b927da66f653..51bee695d32c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1168,6 +1168,9 @@ static int sockmap_get_from_fd(const union bpf_attr *attr, bool attach)
         return 0;
 }
 
+#define BPF_F_ATTACH_MASK \
+        (BPF_F_ALLOW_OVERRIDE | BPF_F_ALLOW_MULTI)
+
 static int bpf_prog_attach(const union bpf_attr *attr)
 {
         enum bpf_prog_type ptype;
@@ -1181,7 +1184,7 @@ static int bpf_prog_attach(const union bpf_attr *attr)
         if (CHECK_ATTR(BPF_PROG_ATTACH))
                 return -EINVAL;
 
-        if (attr->attach_flags & ~BPF_F_ALLOW_OVERRIDE)
+        if (attr->attach_flags & ~BPF_F_ATTACH_MASK)
                 return -EINVAL;
 
         switch (attr->attach_type) {
@@ -1212,8 +1215,8 @@ static int bpf_prog_attach(const union bpf_attr *attr)
                 return PTR_ERR(cgrp);
         }
 
-        ret = cgroup_bpf_update(cgrp, prog, attr->attach_type,
-                                attr->attach_flags & BPF_F_ALLOW_OVERRIDE);
+        ret = cgroup_bpf_attach(cgrp, prog, attr->attach_type,
+                                attr->attach_flags);
         if (ret)
                 bpf_prog_put(prog);
         cgroup_put(cgrp);
@@ -1225,6 +1228,8 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 
 static int bpf_prog_detach(const union bpf_attr *attr)
 {
+        enum bpf_prog_type ptype;
+        struct bpf_prog *prog;
         struct cgroup *cgrp;
         int ret;
 
@@ -1237,23 +1242,33 @@ static int bpf_prog_detach(const union bpf_attr *attr)
         switch (attr->attach_type) {
         case BPF_CGROUP_INET_INGRESS:
         case BPF_CGROUP_INET_EGRESS:
+                ptype = BPF_PROG_TYPE_CGROUP_SKB;
+                break;
         case BPF_CGROUP_INET_SOCK_CREATE:
+                ptype = BPF_PROG_TYPE_CGROUP_SOCK;
+                break;
         case BPF_CGROUP_SOCK_OPS:
-                cgrp = cgroup_get_from_fd(attr->target_fd);
-                if (IS_ERR(cgrp))
-                        return PTR_ERR(cgrp);
-
-                ret = cgroup_bpf_update(cgrp, NULL, attr->attach_type, false);
-                cgroup_put(cgrp);
+                ptype = BPF_PROG_TYPE_SOCK_OPS;
                 break;
         case BPF_SK_SKB_STREAM_PARSER:
         case BPF_SK_SKB_STREAM_VERDICT:
-                ret = sockmap_get_from_fd(attr, false);
-                break;
+                return sockmap_get_from_fd(attr, false);
         default:
                 return -EINVAL;
         }
 
+        cgrp = cgroup_get_from_fd(attr->target_fd);
+        if (IS_ERR(cgrp))
+                return PTR_ERR(cgrp);
+
+        prog = bpf_prog_get_type(attr->attach_bpf_fd, ptype);
+        if (IS_ERR(prog))
+                prog = NULL;
+
+        ret = cgroup_bpf_detach(cgrp, prog, attr->attach_type, 0);
+        if (prog)
+                bpf_prog_put(prog);
+        cgroup_put(cgrp);
         return ret;
 }