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>

1 files changed, 29 insertions, 19 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 8c0553d9afd3..2a06f1fa7001 100644
--- 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;