[PATCH 1/1] kernel/ucounts: expose current inotify watch count

[Albert Vaca Cintora]

Adds a readonly 'current_inotify_watches' entry to the user sysctl table.
The handler for this entry is a custom function that ends calling
proc_dointvec.

Signed-off-by: Albert Vaca Cintora <albertv...@gmail.com>
---
 kernel/ucount.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index f48d1b6376a4..afa3b89e3373 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -57,6 +57,11 @@ static struct ctl_table_root set_root = {
        .permissions = set_permissions,
 };

+#ifdef CONFIG_INOTIFY_USER
+int proc_read_inotify_watches(struct ctl_table *table, int write,
+                    void __user *buffer, size_t *lenp, loff_t *ppos);
+#endif
+
 static int zero = 0;
 static int int_max = INT_MAX;
 #define UCOUNT_ENTRY(name)                             \
@@ -79,6 +84,12 @@ static struct ctl_table user_table[] = {
 #ifdef CONFIG_INOTIFY_USER
        UCOUNT_ENTRY("max_inotify_instances"),
        UCOUNT_ENTRY("max_inotify_watches"),
+       {
+               .procname       = "current_inotify_watches",
+               .maxlen         = sizeof(int),
+               .mode           = 0444,
+               .proc_handler   = proc_read_inotify_watches,
+       },
 #endif
        { }
 };
@@ -226,6 +237,24 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type 
type)
        put_ucounts(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;
+       int count;
+
+       ucounts = get_ucounts(current_user_ns(), current_euid());
+       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);
+}
+#endif
+
 static __init int user_namespace_sysctl_init(void)
 {
 #ifdef CONFIG_SYSCTL
--
2.20.1