linux-kernel - [RFC][PATCH] tracing: Have traceprobe_probes_write() not access userspace unnecessarily

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Date:   Thu, 9 Feb 2017 18:04:58 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
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@...dmis.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