[PATCH bpf v2 2/6] bpf: flow_dissector: check value of unused flags to BPF_PROG_DETACH

[Lorenz Bauer <lmb@cloudflare.com>]

Using BPF_PROG_DETACH on a flow dissector program supports neither
attach_flags nor attach_bpf_fd. Yet no value is enforced for them.

Enforce that attach_flags are zero, and require the current program
to be passed via attach_bpf_fd. This allows us to remove the check
for CAP_SYS_ADMIN, since userspace can now no longer remove
arbitrary flow dissector programs.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Fixes: b27f7bb590ba ("flow_dissector: Move out netns_bpf prog callbacks")
---
 include/linux/bpf-netns.h  |  5 +++--
 kernel/bpf/net_namespace.c | 19 +++++++++++++++----
 kernel/bpf/syscall.c       |  4 +---
 3 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/include/linux/bpf-netns.h b/include/linux/bpf-netns.h
index 4052d649f36d..47d5b0c708c9 100644
--- a/include/linux/bpf-netns.h
+++ b/include/linux/bpf-netns.h
@@ -33,7 +33,7 @@ int netns_bpf_prog_query(const union bpf_attr *attr,
 			 union bpf_attr __user *uattr);
 int netns_bpf_prog_attach(const union bpf_attr *attr,
 			  struct bpf_prog *prog);
-int netns_bpf_prog_detach(const union bpf_attr *attr);
+int netns_bpf_prog_detach(const union bpf_attr *attr, enum bpf_prog_type ptype);
 int netns_bpf_link_create(const union bpf_attr *attr,
 			  struct bpf_prog *prog);
 #else
@@ -49,7 +49,8 @@ static inline int netns_bpf_prog_attach(const union bpf_attr *attr,
 	return -EOPNOTSUPP;
 }
 
-static inline int netns_bpf_prog_detach(const union bpf_attr *attr)
+static inline int netns_bpf_prog_detach(const union bpf_attr *attr,
+					enum bpf_prog_type ptype)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/kernel/bpf/net_namespace.c b/kernel/bpf/net_namespace.c
index bf18eabeaea2..7216215990ed 100644
--- a/kernel/bpf/net_namespace.c
+++ b/kernel/bpf/net_namespace.c
@@ -286,7 +286,8 @@ static void netns_bpf_run_array_detach(struct net *net,
 
 /* Must be called with netns_bpf_mutex held. */
 static int __netns_bpf_prog_detach(struct net *net,
-				   enum netns_bpf_attach_type type)
+				   enum netns_bpf_attach_type type,
+				   struct bpf_prog *old)
 {
 	struct bpf_prog *attached;
 
@@ -295,7 +296,7 @@ static int __netns_bpf_prog_detach(struct net *net,
 		return -EINVAL;
 
 	attached = net->bpf.progs[type];
-	if (!attached)
+	if (!attached || attached != old)
 		return -ENOENT;
 	netns_bpf_run_array_detach(net, type);
 	net->bpf.progs[type] = NULL;
@@ -303,19 +304,29 @@ static int __netns_bpf_prog_detach(struct net *net,
 	return 0;
 }
 
-int netns_bpf_prog_detach(const union bpf_attr *attr)
+int netns_bpf_prog_detach(const union bpf_attr *attr, enum bpf_prog_type ptype)
 {
 	enum netns_bpf_attach_type type;
+	struct bpf_prog *prog;
 	int ret;
 
+	if (attr->target_fd)
+		return -EINVAL;
+
 	type = to_netns_bpf_attach_type(attr->attach_type);
 	if (type < 0)
 		return -EINVAL;
 
+	prog = bpf_prog_get_type(attr->attach_bpf_fd, ptype);
+	if (IS_ERR(prog))
+		return PTR_ERR(prog);
+
 	mutex_lock(&netns_bpf_mutex);
-	ret = __netns_bpf_prog_detach(current->nsproxy->net_ns, type);
+	ret = __netns_bpf_prog_detach(current->nsproxy->net_ns, type, prog);
 	mutex_unlock(&netns_bpf_mutex);
 
+	bpf_prog_put(prog);
+
 	return ret;
 }
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8da159936bab..c0ec572f056c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2897,9 +2897,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
 	case BPF_PROG_TYPE_LIRC_MODE2:
 		return lirc_prog_detach(attr);
 	case BPF_PROG_TYPE_FLOW_DISSECTOR:
-		if (!capable(CAP_NET_ADMIN))
-			return -EPERM;
-		return netns_bpf_prog_detach(attr);
+		return netns_bpf_prog_detach(attr, ptype);
 	case BPF_PROG_TYPE_CGROUP_DEVICE:
 	case BPF_PROG_TYPE_CGROUP_SKB:
 	case BPF_PROG_TYPE_CGROUP_SOCK:
-- 
2.25.1