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 ae62c16e105a ("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: bfe4037e722e ("aio: implement IOCB_CMD_POLL")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reported-by: syzbot+fab6de82892b6b9c6191@syzkaller.appspotmail.com
Reported-by: syzbot+53c0b767f7ca0dc0c451@syzkaller.appspotmail.com
Reported-by: syzbot+a3accb352f9c22041cfa@syzkaller.appspotmail.com
Reviewed-by: Andrew 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ae0b8b5f69e6e205e4d9288df90ee4a2c8f64b69..ccbdbd62f0d8ecf16a19f2f191d5809e317da9d5 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -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