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Subject[for-next-3.11][PATCH 6/9] tracing: Change tracing_fops/snapshot_fops to rely on tracing_get_cpu()
From: Oleg Nesterov <oleg@redhat.com>

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>
---
kernel/trace/trace.c | 50 ++++++++++++++++++++++----------------------------
1 file changed, 22 insertions(+), 28 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 68b4685..dd7780d 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)
--
1.7.10.4



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