tracing: Have traceprobe_probes_write() not access userspace unnecessarily

The code in traceprobe_probes_write() reads up to 4096 bytes from userpace
for each line. If userspace passes in several lines to execute, the code
will do a large read for each line, even though, it is highly likely that
the first read from userspace received all of the lines at once.

I changed the logic to do a single read from userspace, and to only read
from userspace again if not all of the read from userspace made it in.

I tested this by adding printk()s and writing files that would test -1, ==,
and +1 the buffer size, to make sure that there's no overflows and that if a
single line is written with +1 the buffer size, that it fails properly.

Link: http://lkml.kernel.org/r/20170209180458.5c829ab2@gandalf.local.home
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Namhyung Kim <namhyung@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 8c0553d9afd3f2563756641cfa0e659a4ab7ff99..2a06f1fa7001b8d3eab7701ef94026e48467327c 100644 (file)
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -647,7 +647,7 @@ ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
                                size_t count, loff_t *ppos,
                                int (*createfn)(int, char **))
 {
-       char *kbuf, *tmp;
+       char *kbuf, *buf, *tmp;
        int ret = 0;
        size_t done = 0;
        size_t size;
@@ -667,27 +667,37 @@ ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
                        goto out;
                }
                kbuf[size] = '\0';
-               tmp = strchr(kbuf, '\n');
+               buf = kbuf;
+               do {
+                       tmp = strchr(buf, '\n');
+                       if (tmp) {
+                               *tmp = '\0';
+                               size = tmp - buf + 1;
+                       } else {
+                               size = strlen(buf);
+                               if (done + size < count) {
+                                       if (buf != kbuf)
+                                               break;
+                                       pr_warn("Line length is too long: Should be less than %d\n",
+                                               WRITE_BUFSIZE);
+                                       ret = -EINVAL;
+                                       goto out;
+                               }
+                       }
+                       done += size;
 
-               if (tmp) {
-                       *tmp = '\0';
-                       size = tmp - kbuf + 1;
-               } else if (done + size < count) {
-                       pr_warn("Line length is too long: Should be less than %d\n",
-                               WRITE_BUFSIZE);
-                       ret = -EINVAL;
-                       goto out;
-               }
-               done += size;
-               /* Remove comments */
-               tmp = strchr(kbuf, '#');
+                       /* Remove comments */
+                       tmp = strchr(buf, '#');
 
-               if (tmp)
-                       *tmp = '\0';
+                       if (tmp)
+                               *tmp = '\0';
 
-               ret = traceprobe_command(kbuf, createfn);
-               if (ret)
-                       goto out;
+                       ret = traceprobe_command(buf, createfn);
+                       if (ret)
+                               goto out;
+                       buf += size;
+
+               } while (done < count);
        }
        ret = done;