bpf: Fix missing -EFAULT return on user log buf error in btf_parse()

btf_parse() is missing -EFAULT error return if log->ubuf was NULL-ed out
due to error while copying data into user-provided buffer. Add it, but
handle a special case of BPF_LOG_KERNEL in which log->ubuf is always NULL.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Lorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/bpf/20230406234205.323208-9-andrii@kernel.org

kernel/bpf/btf.c

@@ -5598,6 +5598,10 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size,
 		err = -ENOSPC;
 		goto errout_meta;
 	}
+	if (log->level && log->level != BPF_LOG_KERNEL && !log->ubuf) {
+		err = -EFAULT;
+		goto errout_meta;
+	}
 
 	btf_verifier_env_free(env);
 	refcount_set(&btf->refcnt, 1);