On Fri, 31 May 2019 21:50:15 +0200 Albert Vaca Cintora <albertv...@gmail.com>
wrote:
> Adds a readonly 'current_inotify_watches' entry to the user sysctl table.
> The handler for this entry is a custom function that ends up calling
> proc_dointvec. Said sysctl table already contains 'max_inotify_watches'
> and it gets mounted under /proc/sys/user/.
>
> Inotify watches are a finite resource, in a similar way to available file
> descriptors. The motivation for this patch is to be able to set up
> monitoring and alerting before an application starts failing because
> it runs out of inotify watches.
>
> ...
>
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -118,6 +118,26 @@ static void put_ucounts(struct ucounts *ucounts)
> kfree(ucounts);
> }
>
> +#ifdef CONFIG_INOTIFY_USER
> +int proc_read_inotify_watches(struct ctl_table *table, int write,
> + void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> + struct ucounts *ucounts;
> + struct ctl_table fake_table;
hmm.
> + int count = -1;
> +
> + ucounts = get_ucounts(current_user_ns(), current_euid());
> + if (ucounts != NULL) {
> + count = atomic_read(&ucounts->ucount[UCOUNT_INOTIFY_WATCHES]);
> + put_ucounts(ucounts);
> + }
> +
> + fake_table.data = &count;
> + fake_table.maxlen = sizeof(count);
> + return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
proc_dointvec
->do_proc_dointvec
->__do_proc_dointvec
->proc_first_pos_non_zero_ignore
->warn_sysctl_write
->pr_warn_once(..., table->procname)
and I think ->procname is uninitialized.
That's from a cursory check. Perhaps other uninitialized members of
fake_table are accessed, dunno.
we could do
{
struct ctl_table fake_table = {
.data = &count,
.maxlen = sizeof(count),
};
return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
}
or whatever. That will cause the pr_warn_once to print "(null)" but
that's OK I guess.
Are there other places in the kernel which do this temp ctl_table
trick? If so, what do they do? If not, what is special about this
code?
