[PATCH v3 1/5] tracing: Fix checking of freed trace_event_file for hist files

[Petr Pavlu]

The event_hist_open() and event_hist_poll() functions currently retrieve
a trace_event_file pointer from a file struct by invoking
event_file_data(), which simply returns file->f_inode->i_private. The
functions then check if the pointer is NULL to determine whether the event
is still valid. This approach is flawed because i_private is assigned when
an eventfs inode is allocated and remains set throughout its lifetime.
Instead, the code should call event_file_file(), which checks for
EVENT_FILE_FL_FREED. Using the incorrect access function may result in the
code potentially opening a hist file for an event that is being removed or
becoming stuck while polling on this file.

Correct the access method to event_file_file() in both functions.

Fixes: 1bd13edbbed6 ("tracing/hist: Add poll(POLLIN) support on hist file")
Signed-off-by: Petr Pavlu <petr.pa...@suse.com>
Acked-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
 kernel/trace/trace_events_hist.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index e6f449f53afc..768df987419e 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5784,7 +5784,7 @@ static __poll_t event_hist_poll(struct file *file, struct 
poll_table_struct *wai
 
        guard(mutex)(&event_mutex);
 
-       event_file = event_file_data(file);
+       event_file = event_file_file(file);
        if (!event_file)
                return EPOLLERR;
 
@@ -5822,7 +5822,7 @@ static int event_hist_open(struct inode *inode, struct 
file *file)
 
        guard(mutex)(&event_mutex);
 
-       event_file = event_file_data(file);
+       event_file = event_file_file(file);
        if (!event_file) {
                ret = -ENODEV;
                goto err;
-- 
2.53.0