Commit e9aba515 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Greg Kroah-Hartman
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tty: rework pty count limiting 



After adding devpts multiple-insrances sysctl kernel.pty.max limit pty count for
each devpts instance independently, while kernel.pty.nr shows total pty count.

This patch restores sysctl kernel.pty.max as global limit (4096 by default),
adds pty reseve for main devpts (mounted without "newinstance" argument),
and new sysctl to tune it: kernel.pty.reserve (1024 by default)

Also it adds devpts mount option "max=%d" to limit pty count for each devpts
instance independently. (by default NR_UNIX98_PTY_MAX == 2^20)

Thus devpts instances in containers cannot eat up all available pty even if we didn't
set any limits, while with "max" argument we can adjust limits more precisely.

Plus, now open("/dev/ptmx") return -ENOSPC in case lack of pty indexes,
this is more informative than -EIO.

Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent a4834c10

fs/devpts/inode.c

+30 −4
Original line number Original line Diff line number Diff line
@@ -41,8 +41,9 @@ 
 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.

 * 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 = NR_UNIX98_PTY_DEFAULT;

static int pty_reserve = NR_UNIX98_PTY_RESERVE;

static int pty_limit_min;

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 int pty_count;





static struct ctl_table pty_table[] = {

static struct ctl_table pty_table[] = {
@@ -54,6 +55,14 @@ static struct ctl_table pty_table[] = { 
		.proc_handler	= proc_dointvec_minmax,

		.proc_handler	= proc_dointvec_minmax,

		.extra1		= &pty_limit_min,

		.extra1		= &pty_limit_min,

		.extra2		= &pty_limit_max,

		.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",

		.procname	= "nr",

		.maxlen		= sizeof(int),

		.maxlen		= sizeof(int),
@@ -94,10 +103,11 @@ struct pts_mount_opts { 
	umode_t mode;

	umode_t mode;

	umode_t ptmxmode;

	umode_t ptmxmode;

	int newinstance;

	int newinstance;

	int max;

};

};





enum {

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

	Opt_err

};

};
@@ -108,6 +118,7 @@ static const match_table_t tokens = { 
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES

#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES

	{Opt_ptmxmode, "ptmxmode=%o"},

	{Opt_ptmxmode, "ptmxmode=%o"},

	{Opt_newinstance, "newinstance"},

	{Opt_newinstance, "newinstance"},

	{Opt_max, "max=%d"},

#endif

#endif

	{Opt_err, NULL}

	{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->gid     = 0;

	opts->mode    = DEVPTS_DEFAULT_MODE;

	opts->mode    = DEVPTS_DEFAULT_MODE;

	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

	opts->max     = NR_UNIX98_PTY_MAX;





	/* newinstance makes sense only on initial mount */

	/* newinstance makes sense only on initial mount */

	if (op == PARSE_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)

			if (op == PARSE_MOUNT)

				opts->newinstance = 1;

				opts->newinstance = 1;

			break;

			break;

		case Opt_max:

			if (match_int(&args[0], &option) ||

			    option < 0 || option > NR_UNIX98_PTY_MAX)

				return -EINVAL;

			opts->max = option;

			break;

#endif

#endif

		default:

		default:

			printk(KERN_ERR "devpts: called with bogus options\n");

			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);

	seq_printf(seq, ",mode=%03o", opts->mode);

#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES

#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES

	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);

	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);

	if (opts->max < NR_UNIX98_PTY_MAX)

		seq_printf(seq, ",max=%d", opts->max);

#endif

#endif





	return 0;

	return 0;
@@ -483,6 +503,12 @@ retry: 
		return -ENOMEM;

		return -ENOMEM;





	mutex_lock(&allocated_ptys_lock);

	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);

	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);

	if (ida_ret < 0) {

	if (ida_ret < 0) {

		mutex_unlock(&allocated_ptys_lock);

		mutex_unlock(&allocated_ptys_lock);
@@ -491,10 +517,10 @@ retry: 
		return -EIO;

		return -EIO;

	}

	}





	if (index >= pty_limit) {

	if (index >= fsi->mount_opts.max) {

		ida_remove(&fsi->allocated_ptys, index);

		ida_remove(&fsi->allocated_ptys, index);

		mutex_unlock(&allocated_ptys_lock);

		mutex_unlock(&allocated_ptys_lock);

		return -EIO;

		return -ENOSPC;

	}

	}

	pty_count++;

	pty_count++;

	mutex_unlock(&allocated_ptys_lock);

	mutex_unlock(&allocated_ptys_lock);

include/linux/tty.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -52,6 +52,7 @@ 
 * hardcoded at present.)

 * hardcoded at present.)

 */

 */

#define NR_UNIX98_PTY_DEFAULT	4096      /* Default maximum for Unix98 ptys */

#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 */

#define NR_UNIX98_PTY_MAX	(1 << MINORBITS) /* Absolute limit */





/*

/*

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