On Fri, Jul 24, 2020 at 10:22:36PM -0700, Pascal Bouchareine wrote:
> This command attaches a description to a file descriptor for
> troubleshooting purposes. The free string is displayed in the
> process fdinfo file for that fd /proc/pid/fdinfo/fd.
>
> One intended usage is to allow processes to self-document sockets
> for netstat and friends to report
> +static long fcntl_set_description(struct file *file, char __user *desc)
> +{
> + char *d;
> +
> + d = strndup_user(desc, MAX_FILE_DESC_SIZE);
This should be kmem accounted because allocation is persistent.
To make things more entertaining, strndup_user() doesn't have gfp_t argument.
> + if (IS_ERR(d))
> + return PTR_ERR(d);
> +
> + spin_lock(&file->f_lock);
> + kfree(file->f_description);
> + file->f_description = d;
> + spin_unlock(&file->f_lock);
Generally kfree under spinlock is not good idea.
You can replace the pointer and free without spinlock.
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -980,6 +980,9 @@ struct file {
> struct address_space *f_mapping;
> errseq_t f_wb_err;
> errseq_t f_sb_err; /* for syncfs */
> +
> +#define MAX_FILE_DESC_SIZE 256
> + char *f_description;
struct file is nicely aligned to 256 bytes on distro configs.
Will this break everything?
$ cat /sys/kernel/slab/filp/object_size
