bpf: introduce BPF_F_ALLOW_OVERRIDE flag

If BPF_F_ALLOW_OVERRIDE flag is used in BPF_PROG_ATTACH command
to the given cgroup the descendent cgroup will be able to override
effective bpf program that was inherited from this cgroup.
By default it's not passed, therefore override is disallowed.

Examples:
1.
prog X attached to /A with default
prog Y fails to attach to /A/B and /A/B/C
Everything under /A runs prog X

2.
prog X attached to /A with allow_override.
prog Y fails to attach to /A/B with default (non-override)
prog M attached to /A/B with allow_override.
Everything under /A/B runs prog M only.

3.
prog X attached to /A with allow_override.
prog Y fails to attach to /A with default.
The user has to detach first to switch the mode.

In the future this behavior may be extended with a chain of
non-overridable programs.

Also fix the bug where detach from cgroup where nothing is attached
was not throwing error. Return ENOENT in such case.

Add several testcases and adjust libbpf.

Fixes: 3007098494be ("cgroup: add support for eBPF programs")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 6 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 19b6129eab23..bbb016adbaeb 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -920,13 +920,14 @@ static int bpf_obj_get(const union bpf_attr *attr)
 
 #ifdef CONFIG_CGROUP_BPF
 
-#define BPF_PROG_ATTACH_LAST_FIELD attach_type
+#define BPF_PROG_ATTACH_LAST_FIELD attach_flags
 
 static int bpf_prog_attach(const union bpf_attr *attr)
 {
+        enum bpf_prog_type ptype;
         struct bpf_prog *prog;
         struct cgroup *cgrp;
-        enum bpf_prog_type ptype;
+        int ret;
 
         if (!capable(CAP_NET_ADMIN))
                 return -EPERM;
@@ -934,6 +935,9 @@ 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)
+                return -EINVAL;
+
         switch (attr->attach_type) {
         case BPF_CGROUP_INET_INGRESS:
         case BPF_CGROUP_INET_EGRESS:
@@ -956,10 +960,13 @@ static int bpf_prog_attach(const union bpf_attr *attr)
                 return PTR_ERR(cgrp);
         }
 
-        cgroup_bpf_update(cgrp, prog, attr->attach_type);
+        ret = cgroup_bpf_update(cgrp, prog, attr->attach_type,
+                                attr->attach_flags & BPF_F_ALLOW_OVERRIDE);
+        if (ret)
+                bpf_prog_put(prog);
         cgroup_put(cgrp);
 
-        return 0;
+        return ret;
 }
 
 #define BPF_PROG_DETACH_LAST_FIELD attach_type
@@ -967,6 +974,7 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 static int bpf_prog_detach(const union bpf_attr *attr)
 {
         struct cgroup *cgrp;
+        int ret;
 
         if (!capable(CAP_NET_ADMIN))
                 return -EPERM;
@@ -982,7 +990,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
                 if (IS_ERR(cgrp))
                         return PTR_ERR(cgrp);
 
-                cgroup_bpf_update(cgrp, NULL, attr->attach_type);
+                ret = cgroup_bpf_update(cgrp, NULL, attr->attach_type, false);
                 cgroup_put(cgrp);
                 break;
 
@@ -990,7 +998,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
                 return -EINVAL;
         }
 
-        return 0;
+        return ret;
 }
 #endif /* CONFIG_CGROUP_BPF */