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Subject[RFC][PATCH] 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 one.

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.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_probe.c | 48 ++++++++++++++++++++++++++++------------------
1 file changed, 29 insertions(+), 19 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 8c0553d..2a06f1f 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;

--
2.9.3
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