[PATCH bpf] bpf: fix TCX/netkit detach permissions when prog FD isn't given

[Guillaume GONNET <ggonnet.linux@gmail.com>]

This commit fixes a security issue where BPF_PROG_DETACH on TCX or netkit
devices could be executed by any user when no program FD was provided,
bypassing permission checks. The fix adds a capability check for
CAP_NET_ADMIN or CAP_SYS_ADMIN in this case.

Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support")
Signed-off-by: Guillaume GONNET <ggonnet.linux@gmail.com>
---
 include/linux/bpf.h       |  5 +++++
 include/linux/bpf_mprog.h | 10 ++++++++++
 kernel/bpf/syscall.c      |  7 ++-----
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4427c6e98331..5f59d1f173a2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2742,6 +2742,11 @@ static inline bool bpf_bypass_spec_v4(const struct bpf_token *token)
 		bpf_token_capable(token, CAP_PERFMON);
 }
 
+static inline bool bpf_net_capable(void)
+{
+	return capable(CAP_NET_ADMIN) || capable(CAP_SYS_ADMIN);
+}
+
 int bpf_map_new_fd(struct bpf_map *map, int flags);
 int bpf_prog_new_fd(struct bpf_prog *prog);
 
diff --git a/include/linux/bpf_mprog.h b/include/linux/bpf_mprog.h
index 929225f7b095..0b9f4caeeb0a 100644
--- a/include/linux/bpf_mprog.h
+++ b/include/linux/bpf_mprog.h
@@ -340,4 +340,14 @@ static inline bool bpf_mprog_supported(enum bpf_prog_type type)
 		return false;
 	}
 }
+
+static inline bool bpf_mprog_detach_empty(enum bpf_prog_type type)
+{
+	switch (type) {
+	case BPF_PROG_TYPE_SCHED_CLS:
+		return bpf_net_capable();
+	default:
+		return false;
+	}
+}
 #endif /* __BPF_MPROG_H */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b9184545c3fd..419d88bb5944 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1363,11 +1363,6 @@ static int map_check_btf(struct bpf_map *map, struct bpf_token *token,
 	return ret;
 }
 
-static bool bpf_net_capable(void)
-{
-	return capable(CAP_NET_ADMIN) || capable(CAP_SYS_ADMIN);
-}
-
 #define BPF_MAP_CREATE_LAST_FIELD excl_prog_hash_size
 /* called via syscall */
 static int map_create(union bpf_attr *attr, bpfptr_t uattr)
@@ -4579,6 +4574,8 @@ static int bpf_prog_detach(const union bpf_attr *attr)
 			prog = bpf_prog_get_type(attr->attach_bpf_fd, ptype);
 			if (IS_ERR(prog))
 				return PTR_ERR(prog);
+		} else if (!bpf_mprog_detach_empty(ptype))
+			return -EPERM;
 		}
 	} else if (is_cgroup_prog_type(ptype, 0, false)) {
 		if (attr->attach_flags || attr->relative_fd)
-- 
2.34.1