tracing: Change tracing_fops/snapshot_fops to rely on tracing_get_cpu()

tracing_open() and tracing_snapshot_open() are racy, the memory
inode->i_private points to can be already freed.

Convert these last users of "inode->i_private == trace_cpu" to
use "i_private = trace_array" and rely on tracing_get_cpu().

v2: incorporate the fix from Steven, tracing_release() must not
    blindly dereference file->private_data unless we know that
    the file was opened for reading.

Link: http://lkml.kernel.org/r/20130723152610.GA23737@redhat.com

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 22 insertions, 28 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 68b46851666f..dd7780ddde08 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2862,9 +2862,9 @@ static const struct seq_operations tracer_seq_ops = {
 };
 
 static struct trace_iterator *
-__tracing_open(struct trace_array *tr, struct trace_cpu *tc,
-               struct inode *inode, struct file *file, bool snapshot)
+__tracing_open(struct inode *inode, struct file *file, bool snapshot)
 {
+        struct trace_array *tr = inode->i_private;
         struct trace_iterator *iter;
         int cpu;
 
@@ -2905,8 +2905,8 @@ __tracing_open(struct trace_array *tr, struct trace_cpu *tc,
                 iter->trace_buffer = &tr->trace_buffer;
         iter->snapshot = snapshot;
         iter->pos = -1;
+        iter->cpu_file = tracing_get_cpu(inode);
         mutex_init(&iter->mutex);
-        iter->cpu_file = tc->cpu;
 
         /* Notify the tracer early; before we stop tracing. */
         if (iter->trace && iter->trace->open)
@@ -2986,22 +2986,18 @@ static int tracing_open_generic_tr(struct inode *inode, struct file *filp)
 
 static int tracing_release(struct inode *inode, struct file *file)
 {
+        struct trace_array *tr = inode->i_private;
         struct seq_file *m = file->private_data;
         struct trace_iterator *iter;
-        struct trace_array *tr;
         int cpu;
 
-        /* Writes do not use seq_file, need to grab tr from inode */
         if (!(file->f_mode & FMODE_READ)) {
-                struct trace_cpu *tc = inode->i_private;
-
-                trace_array_put(tc->tr);
+                trace_array_put(tr);
                 return 0;
         }
 
+        /* Writes do not use seq_file */
         iter = m->private;
-        tr = iter->tr;
-
         mutex_lock(&trace_types_lock);
 
         for_each_tracing_cpu(cpu) {
@@ -3048,8 +3044,7 @@ static int tracing_single_release_tr(struct inode *inode, struct file *file)
 
 static int tracing_open(struct inode *inode, struct file *file)
 {
-        struct trace_cpu *tc = inode->i_private;
-        struct trace_array *tr = tc->tr;
+        struct trace_array *tr = inode->i_private;
         struct trace_iterator *iter;
         int ret = 0;
 
@@ -3057,16 +3052,17 @@ static int tracing_open(struct inode *inode, struct file *file)
                 return -ENODEV;
 
         /* If this file was open for write, then erase contents */
-        if ((file->f_mode & FMODE_WRITE) &&
-            (file->f_flags & O_TRUNC)) {
-                if (tc->cpu == RING_BUFFER_ALL_CPUS)
+        if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
+                int cpu = tracing_get_cpu(inode);
+
+                if (cpu == RING_BUFFER_ALL_CPUS)
                         tracing_reset_online_cpus(&tr->trace_buffer);
                 else
-                        tracing_reset(&tr->trace_buffer, tc->cpu);
+                        tracing_reset(&tr->trace_buffer, cpu);
         }
 
         if (file->f_mode & FMODE_READ) {
-                iter = __tracing_open(tr, tc, inode, file, false);
+                iter = __tracing_open(inode, file, false);
                 if (IS_ERR(iter))
                         ret = PTR_ERR(iter);
                 else if (trace_flags & TRACE_ITER_LATENCY_FMT)
@@ -4680,8 +4676,7 @@ struct ftrace_buffer_info {
 #ifdef CONFIG_TRACER_SNAPSHOT
 static int tracing_snapshot_open(struct inode *inode, struct file *file)
 {
-        struct trace_cpu *tc = inode->i_private;
-        struct trace_array *tr = tc->tr;
+        struct trace_array *tr = inode->i_private;
         struct trace_iterator *iter;
         struct seq_file *m;
         int ret = 0;
@@ -4690,7 +4685,7 @@ static int tracing_snapshot_open(struct inode *inode, struct file *file)
                 return -ENODEV;
 
         if (file->f_mode & FMODE_READ) {
-                iter = __tracing_open(tr, tc, inode, file, true);
+                iter = __tracing_open(inode, file, true);
                 if (IS_ERR(iter))
                         ret = PTR_ERR(iter);
         } else {
@@ -4707,8 +4702,8 @@ static int tracing_snapshot_open(struct inode *inode, struct file *file)
                 ret = 0;
 
                 iter->tr = tr;
-                iter->trace_buffer = &tc->tr->max_buffer;
-                iter->cpu_file = tc->cpu;
+                iter->trace_buffer = &tr->max_buffer;
+                iter->cpu_file = tracing_get_cpu(inode);
                 m->private = iter;
                 file->private_data = m;
         }
@@ -5525,7 +5520,6 @@ trace_create_cpu_file(const char *name, umode_t mode, struct dentry *parent,
 static void
 tracing_init_debugfs_percpu(struct trace_array *tr, long cpu)
 {
-        struct trace_array_cpu *data = per_cpu_ptr(tr->trace_buffer.data, cpu);
         struct dentry *d_percpu = tracing_dentry_percpu(tr, cpu);
         struct dentry *d_cpu;
         char cpu_dir[30]; /* 30 characters should be more than enough */
@@ -5546,7 +5540,7 @@ tracing_init_debugfs_percpu(struct trace_array *tr, long cpu)
 
         /* per cpu trace */
         trace_create_cpu_file("trace", 0644, d_cpu,
-                                &data->trace_cpu, cpu, &tracing_fops);
+                                tr, cpu, &tracing_fops);
 
         trace_create_cpu_file("trace_pipe_raw", 0444, d_cpu,
                                 tr, cpu, &tracing_buffers_fops);
@@ -5559,7 +5553,7 @@ tracing_init_debugfs_percpu(struct trace_array *tr, long cpu)
 
 #ifdef CONFIG_TRACER_SNAPSHOT
         trace_create_cpu_file("snapshot", 0644, d_cpu,
-                                &data->trace_cpu, cpu, &snapshot_fops);
+                                tr, cpu, &snapshot_fops);
 
         trace_create_cpu_file("snapshot_raw", 0444, d_cpu,
                                 tr, cpu, &snapshot_raw_fops);
@@ -6125,7 +6119,7 @@ init_tracer_debugfs(struct trace_array *tr, struct dentry *d_tracer)
                           tr, &tracing_iter_fops);
 
         trace_create_file("trace", 0644, d_tracer,
-                        (void *)&tr->trace_cpu, &tracing_fops);
+                          tr, &tracing_fops);
 
         trace_create_file("trace_pipe", 0444, d_tracer,
                           tr, &tracing_pipe_fops);
@@ -6146,11 +6140,11 @@ init_tracer_debugfs(struct trace_array *tr, struct dentry *d_tracer)
                           &trace_clock_fops);
 
         trace_create_file("tracing_on", 0644, d_tracer,
-                            tr, &rb_simple_fops);
+                          tr, &rb_simple_fops);
 
 #ifdef CONFIG_TRACER_SNAPSHOT
         trace_create_file("snapshot", 0644, d_tracer,
-                          (void *)&tr->trace_cpu, &snapshot_fops);
+                          tr, &snapshot_fops);
 #endif
 
         for_each_tracing_cpu(cpu)