Commit cbcfa130 authored by Eric Biggers's avatar Eric Biggers Committed by Linus Torvalds
Browse files

fs/userfaultfd.c: disable irqs for fault_pending and event locks 

When IOCB_CMD_POLL is used on a userfaultfd, aio_poll() disables IRQs
and takes kioctx::ctx_lock, then userfaultfd_ctx::fd_wqh.lock.

This may have to wait for userfaultfd_ctx::fd_wqh.lock to be released by
userfaultfd_ctx_read(), which in turn can be waiting for
userfaultfd_ctx::fault_pending_wqh.lock or
userfaultfd_ctx::event_wqh.lock.

But elsewhere the fault_pending_wqh and event_wqh locks are taken with
IRQs enabled.  Since the IRQ handler may take kioctx::ctx_lock, lockdep
reports that a deadlock is possible.

Fix it by always disabling IRQs when taking the fault_pending_wqh and
event_wqh locks.

Commit ae62c16e ("userfaultfd: disable irqs when taking the
waitqueue lock") didn't fix this because it only accounted for the
fd_wqh lock, not the other locks nested inside it.

Link: http://lkml.kernel.org/r/20190627075004.21259-1-ebiggers@kernel.org


Fixes: bfe4037e ("aio: implement IOCB_CMD_POLL")
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Reported-by: default avatar <syzbot+fab6de82892b6b9c6191@syzkaller.appspotmail.com>
Reported-by: default avatar <syzbot+53c0b767f7ca0dc0c451@syzkaller.appspotmail.com>
Reported-by: default avatar <syzbot+a3accb352f9c22041cfa@syzkaller.appspotmail.com>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>	[4.19+]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b9705d87

fs/userfaultfd.c

+26 −16
Original line number Diff line number Diff line
@@ -40,6 +40,16 @@ enum userfaultfd_state { 
/*

 * Start with fault_pending_wqh and fault_wqh so they're more likely

 * to be in the same cacheline.

 *

 * Locking order:

 *	fd_wqh.lock

 *		fault_pending_wqh.lock

 *			fault_wqh.lock

 *		event_wqh.lock

 *

 * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,

 * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's

 * also taken in IRQ context.

 */

struct userfaultfd_ctx {

	/* waitqueue head for the pending (i.e. not read) userfaults */
@@ -458,7 +468,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) 
	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :

			 TASK_KILLABLE;



	spin_lock(&ctx->fault_pending_wqh.lock);

	spin_lock_irq(&ctx->fault_pending_wqh.lock);

	/*

	 * After the __add_wait_queue the uwq is visible to userland

	 * through poll/read().
@@ -470,7 +480,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) 
	 * __add_wait_queue.

	 */

	set_current_state(blocking_state);

	spin_unlock(&ctx->fault_pending_wqh.lock);

	spin_unlock_irq(&ctx->fault_pending_wqh.lock);



	if (!is_vm_hugetlb_page(vmf->vma))

		must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
@@ -552,13 +562,13 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) 
	 * kernel stack can be released after the list_del_init.

	 */

	if (!list_empty_careful(&uwq.wq.entry)) {

		spin_lock(&ctx->fault_pending_wqh.lock);

		spin_lock_irq(&ctx->fault_pending_wqh.lock);

		/*

		 * No need of list_del_init(), the uwq on the stack

		 * will be freed shortly anyway.

		 */

		list_del(&uwq.wq.entry);

		spin_unlock(&ctx->fault_pending_wqh.lock);

		spin_unlock_irq(&ctx->fault_pending_wqh.lock);

	}



	/*
@@ -583,7 +593,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, 
	init_waitqueue_entry(&ewq->wq, current);

	release_new_ctx = NULL;



	spin_lock(&ctx->event_wqh.lock);

	spin_lock_irq(&ctx->event_wqh.lock);

	/*

	 * After the __add_wait_queue the uwq is visible to userland

	 * through poll/read().
@@ -613,15 +623,15 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, 
			break;

		}



		spin_unlock(&ctx->event_wqh.lock);

		spin_unlock_irq(&ctx->event_wqh.lock);



		wake_up_poll(&ctx->fd_wqh, EPOLLIN);

		schedule();



		spin_lock(&ctx->event_wqh.lock);

		spin_lock_irq(&ctx->event_wqh.lock);

	}

	__set_current_state(TASK_RUNNING);

	spin_unlock(&ctx->event_wqh.lock);

	spin_unlock_irq(&ctx->event_wqh.lock);



	if (release_new_ctx) {

		struct vm_area_struct *vma;
@@ -918,10 +928,10 @@ wakeup: 
	 * the last page faults that may have been already waiting on

	 * the fault_*wqh.

	 */

	spin_lock(&ctx->fault_pending_wqh.lock);

	spin_lock_irq(&ctx->fault_pending_wqh.lock);

	__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);

	__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);

	spin_unlock(&ctx->fault_pending_wqh.lock);

	spin_unlock_irq(&ctx->fault_pending_wqh.lock);



	/* Flush pending events that may still wait on event_wqh */

	wake_up_all(&ctx->event_wqh);
@@ -1134,7 +1144,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, 


	if (!ret && msg->event == UFFD_EVENT_FORK) {

		ret = resolve_userfault_fork(ctx, fork_nctx, msg);

		spin_lock(&ctx->event_wqh.lock);

		spin_lock_irq(&ctx->event_wqh.lock);

		if (!list_empty(&fork_event)) {

			/*

			 * The fork thread didn't abort, so we can
@@ -1180,7 +1190,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, 
			if (ret)

				userfaultfd_ctx_put(fork_nctx);

		}

		spin_unlock(&ctx->event_wqh.lock);

		spin_unlock_irq(&ctx->event_wqh.lock);

	}



	return ret;
@@ -1219,14 +1229,14 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf, 
static void __wake_userfault(struct userfaultfd_ctx *ctx,

			     struct userfaultfd_wake_range *range)

{

	spin_lock(&ctx->fault_pending_wqh.lock);

	spin_lock_irq(&ctx->fault_pending_wqh.lock);

	/* wake all in the range and autoremove */

	if (waitqueue_active(&ctx->fault_pending_wqh))

		__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,

				     range);

	if (waitqueue_active(&ctx->fault_wqh))

		__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);

	spin_unlock(&ctx->fault_pending_wqh.lock);

	spin_unlock_irq(&ctx->fault_pending_wqh.lock);

}



static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
@@ -1881,7 +1891,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) 
	wait_queue_entry_t *wq;

	unsigned long pending = 0, total = 0;



	spin_lock(&ctx->fault_pending_wqh.lock);

	spin_lock_irq(&ctx->fault_pending_wqh.lock);

	list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {

		pending++;

		total++;
@@ -1889,7 +1899,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) 
	list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {

		total++;

	}

	spin_unlock(&ctx->fault_pending_wqh.lock);

	spin_unlock_irq(&ctx->fault_pending_wqh.lock);



	/*

	 * If more protocols will be added, there will be all shown

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