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    Subject[061/102] tracing: Have "enable" file use refcounts like the "filter" file
    3.0-stable review patch.  If anyone has any objections, please let us know.

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

    From: Steven Rostedt <srostedt@redhat.com>

    commit 40ee4dffff061399eb9358e0c8fcfbaf8de4c8fe upstream.

    The "enable" file for the event system can be removed when a module
    is unloaded and the event system only has events from that module.
    As the event system nr_events count goes to zero, it may be freed
    if its ref_count is also set to zero.

    Like the "filter" file, the "enable" file may be opened by a task and
    referenced later, after a module has been unloaded and the events for
    that event system have been removed.

    Although the "filter" file referenced the event system structure,
    the "enable" file only references a pointer to the event system
    name. Since the name is freed when the event system is removed,
    it is possible that an access to the "enable" file may reference
    a freed pointer.

    Update the "enable" file to use the subsystem_open() routine that
    the "filter" file uses, to keep a reference to the event system
    structure while the "enable" file is opened.

    Reported-by: Johannes Berg <johannes.berg@intel.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    kernel/trace/trace_events.c | 31 ++++++++++++++++++++++---------
    1 file changed, 22 insertions(+), 9 deletions(-)

    --- a/kernel/trace/trace_events.c
    +++ b/kernel/trace/trace_events.c
    @@ -557,7 +557,7 @@ system_enable_read(struct file *filp, ch
    loff_t *ppos)
    {
    const char set_to_char[4] = { '?', '0', '1', 'X' };
    - const char *system = filp->private_data;
    + struct event_subsystem *system = filp->private_data;
    struct ftrace_event_call *call;
    char buf[2];
    int set = 0;
    @@ -568,7 +568,7 @@ system_enable_read(struct file *filp, ch
    if (!call->name || !call->class || !call->class->reg)
    continue;

    - if (system && strcmp(call->class->system, system) != 0)
    + if (system && strcmp(call->class->system, system->name) != 0)
    continue;

    /*
    @@ -598,7 +598,8 @@ static ssize_t
    system_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
    loff_t *ppos)
    {
    - const char *system = filp->private_data;
    + struct event_subsystem *system = filp->private_data;
    + const char *name = NULL;
    unsigned long val;
    char buf[64];
    ssize_t ret;
    @@ -622,7 +623,14 @@ system_enable_write(struct file *filp, c
    if (val != 0 && val != 1)
    return -EINVAL;

    - ret = __ftrace_set_clr_event(NULL, system, NULL, val);
    + /*
    + * Opening of "enable" adds a ref count to system,
    + * so the name is safe to use.
    + */
    + if (system)
    + name = system->name;
    +
    + ret = __ftrace_set_clr_event(NULL, name, NULL, val);
    if (ret)
    goto out;

    @@ -862,6 +870,9 @@ static int subsystem_open(struct inode *
    struct event_subsystem *system = NULL;
    int ret;

    + if (!inode->i_private)
    + goto skip_search;
    +
    /* Make sure the system still exists */
    mutex_lock(&event_mutex);
    list_for_each_entry(system, &event_subsystems, list) {
    @@ -880,8 +891,9 @@ static int subsystem_open(struct inode *
    if (system != inode->i_private)
    return -ENODEV;

    + skip_search:
    ret = tracing_open_generic(inode, filp);
    - if (ret < 0)
    + if (ret < 0 && system)
    put_system(system);

    return ret;
    @@ -891,7 +903,8 @@ static int subsystem_release(struct inod
    {
    struct event_subsystem *system = inode->i_private;

    - put_system(system);
    + if (system)
    + put_system(system);

    return 0;
    }
    @@ -1041,10 +1054,11 @@ static const struct file_operations ftra
    };

    static const struct file_operations ftrace_system_enable_fops = {
    - .open = tracing_open_generic,
    + .open = subsystem_open,
    .read = system_enable_read,
    .write = system_enable_write,
    .llseek = default_llseek,
    + .release = subsystem_release,
    };

    static const struct file_operations ftrace_show_header_fops = {
    @@ -1133,8 +1147,7 @@ event_subsystem_dir(const char *name, st
    "'%s/filter' entry\n", name);
    }

    - trace_create_file("enable", 0644, system->entry,
    - (void *)system->name,
    + trace_create_file("enable", 0644, system->entry, system,
    &ftrace_system_enable_fops);

    return system->entry;



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