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Commit 9df04e1f authored by Davide Libenzi's avatar Davide Libenzi Committed by Linus Torvalds
Browse files

epoll: drop max_user_instances and rely only on max_user_watches 



Linus suggested to put limits where the money is, and max_user_watches
already does that w/out the need of max_user_instances.  That has the
advantage to mitigate the potential DoS while allowing pretty generous
default behavior.

Allowing top 4% of low memory (per user) to be allocated in epoll watches,
we have:

LOMEM    MAX_WATCHES (per user)
512MB    ~178000
1GB      ~356000
2GB      ~712000

A box with 512MB of lomem, will meet some challenge in hitting 180K
watches, socket buffers math teaches us.  No more max_user_instances
limits then.

Signed-off-by: default avatarDavide Libenzi <davidel@xmailserver.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Bron Gondwana <brong@fastmail.fm>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3095eb87

fs/eventpoll.c

+4 −18
Original line number Diff line number Diff line
@@ -234,8 +234,6 @@ struct ep_pqueue { 
/*

 * Configuration options available inside /proc/sys/fs/epoll/

 */

/* Maximum number of epoll devices, per user */

static int max_user_instances __read_mostly;

/* Maximum number of epoll watched descriptors, per user */

static int max_user_watches __read_mostly;
@@ -260,14 +258,6 @@ static struct kmem_cache *pwq_cache __read_mostly; 
static int zero;



ctl_table epoll_table[] = {

	{

		.procname	= "max_user_instances",

		.data		= &max_user_instances,

		.maxlen		= sizeof(int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec_minmax,

		.extra1		= &zero,

	},

	{

		.procname	= "max_user_watches",

		.data		= &max_user_watches,
@@ -491,7 +481,6 @@ static void ep_free(struct eventpoll *ep) 


	mutex_unlock(&epmutex);

	mutex_destroy(&ep->mtx);

	atomic_dec(&ep->user->epoll_devs);

	free_uid(ep->user);

	kfree(ep);

}
@@ -581,10 +570,6 @@ static int ep_alloc(struct eventpoll **pep) 
	struct eventpoll *ep;



	user = get_current_user();

	error = -EMFILE;

	if (unlikely(atomic_read(&user->epoll_devs) >=

			max_user_instances))

		goto free_uid;

	error = -ENOMEM;

	ep = kzalloc(sizeof(*ep), GFP_KERNEL);

	if (unlikely(!ep))
@@ -1141,7 +1126,6 @@ SYSCALL_DEFINE1(epoll_create1, int, flags) 
			      flags & O_CLOEXEC);

	if (fd < 0)

		ep_free(ep);

	atomic_inc(&ep->user->epoll_devs);



error_return:

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
@@ -1366,8 +1350,10 @@ static int __init eventpoll_init(void) 
	struct sysinfo si;



	si_meminfo(&si);

	max_user_instances = 128;

	max_user_watches = (((si.totalram - si.totalhigh) / 32) << PAGE_SHIFT) /

	/*

	 * Allows top 4% of lomem to be allocated for epoll watches (per user).

	 */

	max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /

		EP_ITEM_COST;



	/* Initialize the structure used to perform safe poll wait head wake ups */

include/linux/sched.h

+0 −1
Original line number Diff line number Diff line
@@ -630,7 +630,6 @@ struct user_struct { 
	atomic_t inotify_devs;	/* How many inotify devs does this user have opened? */

#endif

#ifdef CONFIG_EPOLL

	atomic_t epoll_devs;	/* The number of epoll descriptors currently open */

	atomic_t epoll_watches;	/* The number of file descriptors currently watched */

#endif

#ifdef CONFIG_POSIX_MQUEUE