bpf:bpf_seq_printf(): handle potentially unsafe format string better

User the proper helper for kernel or userspace addresses based on
TASK_SIZE instead of the dangerous strncpy_from_unsafe function.
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/trace/bpf_trace.c

@@ -588,15 +588,17 @@ BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
 		}
 
 		if (fmt[i] == 's') {
+			void *unsafe_ptr;
+
 			/* try our best to copy */
 			if (memcpy_cnt >= MAX_SEQ_PRINTF_MAX_MEMCPY) {
 				err = -E2BIG;
 				goto out;
 			}
 
-			err = strncpy_from_unsafe_strict(bufs->buf[memcpy_cnt],
-							 (void *) (long) args[fmt_cnt],
-							 MAX_SEQ_PRINTF_STR_LEN);
+			unsafe_ptr = (void *)(long)args[fmt_cnt];
+			err = strncpy_from_kernel_nofault(bufs->buf[memcpy_cnt],
+					unsafe_ptr, MAX_SEQ_PRINTF_STR_LEN);
 			if (err < 0)
 				bufs->buf[memcpy_cnt][0] = '\0';
 			params[fmt_cnt] = (u64)(long)bufs->buf[memcpy_cnt];