[PATCH 017/102] tracing: Protect tracer flags with trace_types_lock

[Luis Henriques]

3.5.7.10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lingzhu Xiang <lxiang at redhat.com>

commit 69d34da2984c95b33ea21518227e1f9470f11d95 upstream.

Backported for 3.4, 3.0-stable. Moved return to after unlock.

From: "Steven Rostedt (Red Hat)" <rostedt at goodmis.org>

Seems that the tracer flags have never been protected from
synchronous writes. Luckily, admins don't usually modify the
tracing flags via two different tasks. But if scripts were to
be used to modify them, then they could get corrupted.

Move the trace_types_lock that protects against tracers changing
to also protect the flags being set.

Cc: stable at vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Lingzhu Xiang <lxiang at redhat.com>
Reviewed-by: CAI Qian <caiqian at redhat.com>
Signed-off-by: Luis Henriques<luis.henriques at canonical.com>
---
 kernel/trace/trace.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 199f77b..b354405 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2791,7 +2791,7 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 	char buf[64];
 	char *cmp;
 	int neg = 0;
-	int ret;
+	int ret = 0;
 	int i;
 
 	if (cnt >= sizeof(buf))
@@ -2808,6 +2808,8 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 		cmp += 2;
 	}
 
+	mutex_lock(&trace_types_lock);
+
 	for (i = 0; trace_options[i]; i++) {
 		if (strcmp(cmp, trace_options[i]) == 0) {
 			set_tracer_flags(1 << i, !neg);
@@ -2816,13 +2818,13 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 	}
 
 	/* If no option could be set, test the specific tracer options */
-	if (!trace_options[i]) {
-		mutex_lock(&trace_types_lock);
+	if (!trace_options[i])
 		ret = set_tracer_option(current_trace, cmp, neg);
-		mutex_unlock(&trace_types_lock);
-		if (ret)
-			return ret;
-	}
+
+	mutex_unlock(&trace_types_lock);
+
+	if (ret)
+		return ret;
 
 	*ppos += cnt;
 
@@ -4601,7 +4603,10 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 	if (val != 0 && val != 1)
 		return -EINVAL;
+
+	mutex_lock(&trace_types_lock);
 	set_tracer_flags(1 << index, val);
+	mutex_unlock(&trace_types_lock);
 
 	*ppos += cnt;
 
-- 
1.8.1.2