kern/58210: linux_sync_file missing struct file::f_data initialization

[campbell+netbsd%mumble.net@localhost]

>Number:         58210
>Category:       kern
>Synopsis:       linux_sync_file missing struct file::f_data initialization
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Apr 28 15:30:00 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current, 10
>Organization:
Sync Linux/kNetBSD Fileoperations
>Environment:
>Description:
sync_file_create doesn't record a pointer from the struct file to the struct sync_file state -- it just initializes some other members:

     60 	fp->f_type = DTYPE_MISC;
     61 	fp->f_flag = FREAD | FWRITE;
     62 	fp->f_ops = &sync_file_ops;

https://nxr.netbsd.org/xref/src/sys/external/bsd/drm2/linux/linux_sync_file.c?r=1.2#47

So when other operations like sync_file_poll and sync_file_close try to use it, well, it doesn't work very well:

     67 static int
     68 sync_file_close(struct file *fp)
     69 {
     70 	struct sync_file *sf = fp->f_data;
     71 
     72 	if (sf->sf_polling)

https://nxr.netbsd.org/xref/src/sys/external/bsd/drm2/linux/linux_sync_file.c?r=1.2#67

(This linux_sync_file.c draft hasn't seen a lot of use, apparently.)
>How-To-Repeat:
do something that involves sync_files
>Fix:
fp->f_data = sf