bpf: Disallow bpf programs call prog_run command.

The verifier cannot perform sufficient validation of bpf_attr->test.ctx_in
pointer, therefore bpf programs should not be allowed to call BPF_PROG_RUN
command from within the program.
To fix this issue split bpf_sys_bpf() bpf helper into normal kern_sys_bpf()
kernel function that can only be used by the kernel light skeleton directly.
Reported-by: YiFei Zhu <zhuyifei@google.com>
Fixes: b1d18a75 ("bpf: Extend sys_bpf commands for bpf_syscall programs.")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/syscall.c

@@ -5071,9 +5071,6 @@ static bool syscall_prog_is_valid_access(int off, int size,
 
 BPF_CALL_3(bpf_sys_bpf, int, cmd, union bpf_attr *, attr, u32, attr_size)
 {
-	struct bpf_prog * __maybe_unused prog;
-	struct bpf_tramp_run_ctx __maybe_unused run_ctx;
-
 	switch (cmd) {
 	case BPF_MAP_CREATE:
 	case BPF_MAP_UPDATE_ELEM:
@@ -5083,6 +5080,18 @@ BPF_CALL_3(bpf_sys_bpf, int, cmd, union bpf_attr *, attr, u32, attr_size)
 	case BPF_LINK_CREATE:
 	case BPF_RAW_TRACEPOINT_OPEN:
 		break;
+	default:
+		return -EINVAL;
+	}
+	return __sys_bpf(cmd, KERNEL_BPFPTR(attr), attr_size);
+}
+
+int kern_sys_bpf(int cmd, union bpf_attr *attr, unsigned int size)
+{
+	struct bpf_prog * __maybe_unused prog;
+	struct bpf_tramp_run_ctx __maybe_unused run_ctx;
+
+	switch (cmd) {
 #ifdef CONFIG_BPF_JIT /* __bpf_prog_enter_sleepable used by trampoline and JIT */
 	case BPF_PROG_TEST_RUN:
 		if (attr->test.data_in || attr->test.data_out ||
@@ -5113,11 +5122,10 @@ BPF_CALL_3(bpf_sys_bpf, int, cmd, union bpf_attr *, attr, u32, attr_size)
 		return 0;
 #endif
 	default:
-		return -EINVAL;
+		return ____bpf_sys_bpf(cmd, attr, size);
 	}
-	return __sys_bpf(cmd, KERNEL_BPFPTR(attr), attr_size);
 }
-EXPORT_SYMBOL(bpf_sys_bpf);
+EXPORT_SYMBOL(kern_sys_bpf);
 
 static const struct bpf_func_proto bpf_sys_bpf_proto = {
 	.func		= bpf_sys_bpf,

tools/lib/bpf/skel_internal.h

@@ -66,13 +66,13 @@ struct bpf_load_and_run_opts {
 	const char *errstr;
 };
 
-long bpf_sys_bpf(__u32 cmd, void *attr, __u32 attr_size);
+long kern_sys_bpf(__u32 cmd, void *attr, __u32 attr_size);
 
 static inline int skel_sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
 			  unsigned int size)
 {
 #ifdef __KERNEL__
-	return bpf_sys_bpf(cmd, attr, size);
+	return kern_sys_bpf(cmd, attr, size);
 #else
 	return syscall(__NR_bpf, cmd, attr, size);
 #endif