2 files changed, 31 insertions, 4 deletions

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index c2c7317d5687..1c6f908e38ca 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -41,8 +41,9 @@
  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
  */
 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
+static int pty_reserve = NR_UNIX98_PTY_RESERVE;
 static int pty_limit_min;
-static int pty_limit_max = NR_UNIX98_PTY_MAX;
+static int pty_limit_max = INT_MAX;
 static int pty_count;
 
 static struct ctl_table pty_table[] = {
@@ -55,6 +56,14 @@ static struct ctl_table pty_table[] = {
                 .extra1         = &pty_limit_min,
                 .extra2         = &pty_limit_max,
         }, {
+                .procname       = "reserve",
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .data           = &pty_reserve,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &pty_limit_min,
+                .extra2         = &pty_limit_max,
+        }, {
                 .procname       = "nr",
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
@@ -94,10 +103,11 @@ struct pts_mount_opts {
         umode_t mode;
         umode_t ptmxmode;
         int newinstance;
+        int max;
 };
 
 enum {
-        Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
+        Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
         Opt_err
 };
 
@@ -108,6 +118,7 @@ static const match_table_t tokens = {
 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
         {Opt_ptmxmode, "ptmxmode=%o"},
         {Opt_newinstance, "newinstance"},
+        {Opt_max, "max=%d"},
 #endif
         {Opt_err, NULL}
 };
@@ -154,6 +165,7 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
         opts->gid     = 0;
         opts->mode    = DEVPTS_DEFAULT_MODE;
         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
+        opts->max     = NR_UNIX98_PTY_MAX;
 
         /* newinstance makes sense only on initial mount */
         if (op == PARSE_MOUNT)
@@ -197,6 +209,12 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
                         if (op == PARSE_MOUNT)
                                 opts->newinstance = 1;
                         break;
+                case Opt_max:
+                        if (match_int(&args[0], &option) ||
+                            option < 0 || option > NR_UNIX98_PTY_MAX)
+                                return -EINVAL;
+                        opts->max = option;
+                        break;
 #endif
                 default:
                         printk(KERN_ERR "devpts: called with bogus options\n");
@@ -303,6 +321,8 @@ static int devpts_show_options(struct seq_file *seq, struct dentry *root)
         seq_printf(seq, ",mode=%03o", opts->mode);
 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
+        if (opts->max < NR_UNIX98_PTY_MAX)
+                seq_printf(seq, ",max=%d", opts->max);
 #endif
 
         return 0;
@@ -483,6 +503,12 @@ retry:
                 return -ENOMEM;
 
         mutex_lock(&allocated_ptys_lock);
+        if (pty_count >= pty_limit -
+                        (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
+                mutex_unlock(&allocated_ptys_lock);
+                return -ENOSPC;
+        }
+
         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
         if (ida_ret < 0) {
                 mutex_unlock(&allocated_ptys_lock);
@@ -491,10 +517,10 @@ retry:
                 return -EIO;
         }
 
-        if (index >= pty_limit) {
+        if (index >= fsi->mount_opts.max) {
                 ida_remove(&fsi->allocated_ptys, index);
                 mutex_unlock(&allocated_ptys_lock);
-                return -EIO;
+                return -ENOSPC;
         }
         pty_count++;
         mutex_unlock(&allocated_ptys_lock);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index d3ebd765b548..d40774188203 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -52,6 +52,7 @@
  * hardcoded at present.)
  */
 #define NR_UNIX98_PTY_DEFAULT   4096      /* Default maximum for Unix98 ptys */
+#define NR_UNIX98_PTY_RESERVE   1024      /* Default reserve for main devpts */
 #define NR_UNIX98_PTY_MAX       (1 << MINORBITS) /* Absolute limit */
 
 /*