[007/200] Fix racy use of anon_inode_getfd() in perf_event.c

Greg KH
2010-07-01T21:13:37Z

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

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

From: Al Viro <viro@zeniv.linux.org.uk>

commit ea635c64e007061f6468ece5cc9cc62d41d4ecf2 upstream.

once anon_inode_getfd() is called, you can't expect *anything* about
struct file that descriptor points to - another thread might be doing
whatever it likes with descriptor table at that point.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/perf_event.c | 40 ++++++++++++++++++++++------------------
1 file changed, 22 insertions(+), 18 deletions(-)

--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4811,8 +4811,8 @@ SYSCALL_DEFINE5(perf_event_open,
struct perf_event_context *ctx;
struct file *event_file = NULL;
struct file *group_file = NULL;
+ int event_fd;
int fput_needed = 0;
- int fput_needed2 = 0;
int err;

/* for future expandability... */
@@ -4833,12 +4833,18 @@ SYSCALL_DEFINE5(perf_event_open,
return -EINVAL;
}

+ event_fd = get_unused_fd_flags(O_RDWR);
+ if (event_fd < 0)
+ return event_fd;
+
/*
* Get the target context (task or percpu):
*/
ctx = find_get_context(pid, cpu);
- if (IS_ERR(ctx))
- return PTR_ERR(ctx);
+ if (IS_ERR(ctx)) {
+ err = PTR_ERR(ctx);
+ goto err_fd;
+ }

/*
* Look up the group leader (we will attach this event to it):
@@ -4878,13 +4884,11 @@ SYSCALL_DEFINE5(perf_event_open,
if (IS_ERR(event))
goto err_put_context;

- err = anon_inode_getfd("[perf_event]", &perf_fops, event, O_RDWR);
- if (err < 0)
- goto err_free_put_context;
-
- event_file = fget_light(err, &fput_needed2);
- if (!event_file)
+ event_file = anon_inode_getfile("[perf_event]", &perf_fops, event, O_RDWR);
+ if (IS_ERR(event_file)) {
+ err = PTR_ERR(event_file);
goto err_free_put_context;
+ }

if (flags & PERF_FLAG_FD_OUTPUT) {
err = perf_event_set_output(event, group_fd);
@@ -4905,19 +4909,19 @@ SYSCALL_DEFINE5(perf_event_open,
list_add_tail(&event->owner_entry, &current->perf_event_list);
mutex_unlock(&current->perf_event_mutex);

-err_fput_free_put_context:
- fput_light(event_file, fput_needed2);
+ fput_light(group_file, fput_needed);
+ fd_install(event_fd, event_file);
+ return event_fd;

+err_fput_free_put_context:
+ fput(event_file);
err_free_put_context:
- if (err < 0)
- free_event(event);
-
+ free_event(event);
err_put_context:
- if (err < 0)
- put_ctx(ctx);
-
fput_light(group_file, fput_needed);
-
+ put_ctx(ctx);
+err_fd:
+ put_unused_fd(event_fd);
return err;
}