tty: move pty count limiting into devpts

Let's move this stuff to the better place, where we can account pty right in
tty-indexes managing code.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 52 insertions, 1 deletions

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index c4e2a58a2e82..c2c7317d5687 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -36,7 +36,52 @@
 #define DEVPTS_DEFAULT_PTMX_MODE 0000
 #define PTMX_MINOR      2
 
-extern int pty_limit;                   /* Config limit on Unix98 ptys */
+/*
+ * sysctl support for setting limits on the number of Unix98 ptys allocated.
+ * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
+ */
+static int pty_limit = NR_UNIX98_PTY_DEFAULT;
+static int pty_limit_min;
+static int pty_limit_max = NR_UNIX98_PTY_MAX;
+static int pty_count;
+
+static struct ctl_table pty_table[] = {
+        {
+                .procname       = "max",
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .data           = &pty_limit,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &pty_limit_min,
+                .extra2         = &pty_limit_max,
+        }, {
+                .procname       = "nr",
+                .maxlen         = sizeof(int),
+                .mode           = 0444,
+                .data           = &pty_count,
+                .proc_handler   = proc_dointvec,
+        },
+        {}
+};
+
+static struct ctl_table pty_kern_table[] = {
+        {
+                .procname       = "pty",
+                .mode           = 0555,
+                .child          = pty_table,
+        },
+        {}
+};
+
+static struct ctl_table pty_root_table[] = {
+        {
+                .procname       = "kernel",
+                .mode           = 0555,
+                .child          = pty_kern_table,
+        },
+        {}
+};
+
 static DEFINE_MUTEX(allocated_ptys_lock);
 
 static struct vfsmount *devpts_mnt;
@@ -451,6 +496,7 @@ retry:
                 mutex_unlock(&allocated_ptys_lock);
                 return -EIO;
         }
+        pty_count++;
         mutex_unlock(&allocated_ptys_lock);
         return index;
 }
@@ -462,6 +508,7 @@ void devpts_kill_index(struct inode *ptmx_inode, int idx)
 
         mutex_lock(&allocated_ptys_lock);
         ida_remove(&fsi->allocated_ptys, idx);
+        pty_count--;
         mutex_unlock(&allocated_ptys_lock);
 }
 
@@ -558,11 +605,15 @@ void devpts_pty_kill(struct tty_struct *tty)
 static int __init init_devpts_fs(void)
 {
         int err = register_filesystem(&devpts_fs_type);
+        struct ctl_table_header *table;
+
         if (!err) {
+                table = register_sysctl_table(pty_root_table);
                 devpts_mnt = kern_mount(&devpts_fs_type);
                 if (IS_ERR(devpts_mnt)) {
                         err = PTR_ERR(devpts_mnt);
                         unregister_filesystem(&devpts_fs_type);
+                        unregister_sysctl_table(table);
                 }
         }
         return err;