bpf: Keep BPF_PROG_LOAD permission checks clear of validations

Move out flags validation and license checks out of the permission
checks. They were intermingled, which makes subsequent changes harder.
Clean this up: perform straightforward flag validation upfront, and
fetch and check license later, right where we use it. Also consolidate
capabilities check in one block, right after basic attribute sanity
checks.

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Stanislav Fomichev <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

kernel/bpf/syscall.c

···
 	struct btf *attach_btf = NULL;
 	int err;
 	char license[128];
-	bool is_gpl;
 
 	if (CHECK_ATTR(BPF_PROG_LOAD))
 		return -EINVAL;
···
 	    (attr->prog_flags & BPF_F_ANY_ALIGNMENT) &&
 	    !bpf_capable())
 		return -EPERM;
-
-	/* copy eBPF program license from user space */
-	if (strncpy_from_bpfptr(license,
-				make_bpfptr(attr->license, uattr.is_kernel),
-				sizeof(license) - 1) < 0)
-		return -EFAULT;
-	license[sizeof(license) - 1] = 0;
-
-	/* eBPF programs must be GPL compatible to use GPL-ed functions */
-	is_gpl = license_is_gpl_compatible(license);
 
 	/* Intent here is for unprivileged_bpf_disabled to block BPF program
 	 * creation for unprivileged users; other actions depend
···
 			     make_bpfptr(attr->insns, uattr.is_kernel),
 			     bpf_prog_insn_size(prog)) != 0)
 		goto free_prog_sec;
+	/* copy eBPF program license from user space */
+	if (strncpy_from_bpfptr(license,
+				make_bpfptr(attr->license, uattr.is_kernel),
+				sizeof(license) - 1) < 0)
+		goto free_prog_sec;
+	license[sizeof(license) - 1] = 0;
+
+	/* eBPF programs must be GPL compatible to use GPL-ed functions */
+	prog->gpl_compatible = license_is_gpl_compatible(license) ? 1 : 0;
 
 	prog->orig_prog = NULL;
 	prog->jited = 0;
 
 	atomic64_set(&prog->aux->refcnt, 1);
-	prog->gpl_compatible = is_gpl ? 1 : 0;
 
 	if (bpf_prog_is_dev_bound(prog->aux)) {
 		err = bpf_prog_dev_bound_init(prog, attr);