tracing/probes: Fix a warning message to show correct maximum length

Since tracing/*probe_events will accept a probe definition
up to 4096 - 2 ('\n' and '\0') bytes, it must show 4094 instead
of 4096 in warning message.

Note that there is one possible case of exceed 4094. If user
prepare 4096 bytes null-terminated string and syscall write
it with the count == 4095, then it can be accepted. However,
if user puts a '\n' after that, it must rejected.
So IMHO, the warning message should indicate shorter one,
since it is safer.

Link: http://lkml.kernel.org/r/148673290462.2579.7966778294009665632.stgit@devbox
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 11b63328d6fbcc4391b146bcdc7ced685f89dbcf..52478f033f88f2d38315c887406608554c391a32 100644 (file)
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -679,8 +679,9 @@ ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
                                if (done + size < count) {
                                        if (buf != kbuf)
                                                break;
+                                       /* This can accept WRITE_BUFSIZE - 2 ('\n' + '\0') */
                                        pr_warn("Line length is too long: Should be less than %d\n",
-                                               WRITE_BUFSIZE);
+                                               WRITE_BUFSIZE - 2);
                                        ret = -EINVAL;
                                        goto out;
                                }