Commit message: futex: Prevent overflow by strengthen input validation

UBSAN reports signed integer overflow in kernel/futex.c:

 UBSAN: Undefined behaviour in kernel/futex.c:2041:18
 signed integer overflow:
 0 - -2147483648 cannot be represented in type 'int'

Add a sanity check to catch negative values of nr_wake and nr_requeue.

Signed-off-by: Li Jinyue <lijinyue@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: dvhart@infradead.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1513242294-31786-1-git-send-email-lijinyue@huawei.com
CVE: CVE-2018-6927
CWE: CWE-190
Vulnerability description: The futex_requeue function in kernel/futex.c in the Linux kernel before 4.14.15 might allow attackers to cause a denial of service (integer overflow) or possibly have unspecified other impact by triggering a negative wake or requeue value.

Project: linux

static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
{
	unsigned int op =	  (encoded_op & 0x70000000) >> 28;
	unsigned int cmp =	  (encoded_op & 0x0f000000) >> 24;
	int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
	int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
	int oldval, ret;

	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
		if (oparg < 0 || oparg > 31) {
			char comm[sizeof(current->comm)];
			/*
			 * kill this print and return -EINVAL when userspace
			 * is sane again
			 */
			pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
					get_task_comm(comm, current), oparg);
			oparg &= 31;
		}
		oparg = 1 << oparg;
	}

	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
		return -EFAULT;

	ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
	if (ret)
		return ret;

	switch (cmp) {
	case FUTEX_OP_CMP_EQ:
		return oldval == cmparg;
	case FUTEX_OP_CMP_NE:
		return oldval != cmparg;
	case FUTEX_OP_CMP_LT:
		return oldval < cmparg;
	case FUTEX_OP_CMP_GE:
		return oldval >= cmparg;
	case FUTEX_OP_CMP_LE:
		return oldval <= cmparg;
	case FUTEX_OP_CMP_GT:
		return oldval > cmparg;
	default:
		return -ENOSYS;
	}
}

Project: linux
File: futex.c

static struct task_struct *futex_find_get_task(pid_t pid)
{
	struct task_struct *p;

	rcu_read_lock();
	p = find_task_by_vpid(pid);
	if (p)
		get_task_struct(p);

	rcu_read_unlock();

	return p;
}

Project: linux
File: futex.c

static inline void futex_get_mm(union futex_key *key)
{
	mmgrab(key->private.mm);
	/*
	 * Ensure futex_get_mm() implies a full barrier such that
	 * get_futex_key() implies a full barrier. This is relied upon
	 * as smp_mb(); (B), see the ordering comment above.
	 */
	smp_mb__after_atomic();
}

Project: linux
File: futex.c

static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
				struct hrtimer_sleeper *timeout)
{
	/*
	 * The task state is guaranteed to be set before another task can
	 * wake it. set_current_state() is implemented using smp_store_mb() and
	 * queue_me() calls spin_unlock() upon completion, both serializing
	 * access to the hash list and forcing another memory barrier.
	 */
	set_current_state(TASK_INTERRUPTIBLE);
	queue_me(q, hb);

	/* Arm the timer */
	if (timeout)
		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);

	/*
	 * If we have been removed from the hash list, then another task
	 * has tried to wake us, and we can skip the call to schedule().
	 */
	if (likely(!plist_node_empty(&q->list))) {
		/*
		 * If the timer has already expired, current will already be
		 * flagged for rescheduling. Only call schedule if there
		 * is no timeout, or if it has yet to expire.
		 */
		if (!timeout || timeout->task)
			freezable_schedule();
	}
	__set_current_state(TASK_RUNNING);
}

Project: linux

static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
				 u32 val, ktime_t *abs_time, u32 bitset,
				 u32 __user *uaddr2)
{
	struct hrtimer_sleeper timeout, *to = NULL;
	struct futex_pi_state *pi_state = NULL;
	struct rt_mutex_waiter rt_waiter;
	struct futex_hash_bucket *hb;
	union futex_key key2 = FUTEX_KEY_INIT;
	struct futex_q q = futex_q_init;
	int res, ret;

	if (!IS_ENABLED(CONFIG_FUTEX_PI))
		return -ENOSYS;

	if (uaddr == uaddr2)
		return -EINVAL;

	if (!bitset)
		return -EINVAL;

	if (abs_time) {
		to = &timeout;
		hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
				      CLOCK_REALTIME : CLOCK_MONOTONIC,
				      HRTIMER_MODE_ABS);
		hrtimer_init_sleeper(to, current);
		hrtimer_set_expires_range_ns(&to->timer, *abs_time,
					     current->timer_slack_ns);
	}

	/*
	 * The waiter is allocated on our stack, manipulated by the requeue
	 * code while we sleep on uaddr.
	 */
	rt_mutex_init_waiter(&rt_waiter);

	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
	if (unlikely(ret != 0))
		goto out;

	q.bitset = bitset;
	q.rt_waiter = &rt_waiter;
	q.requeue_pi_key = &key2;

	/*
	 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
	 * count.
	 */
	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
	if (ret)
		goto out_key2;

	/*
	 * The check above which compares uaddrs is not sufficient for
	 * shared futexes. We need to compare the keys:
	 */
	if (match_futex(&q.key, &key2)) {
		queue_unlock(hb);
		ret = -EINVAL;
		goto out_put_keys;
	}

	/* Queue the futex_q, drop the hb lock, wait for wakeup. */
	futex_wait_queue_me(hb, &q, to);

	spin_lock(&hb->lock);
	ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
	spin_unlock(&hb->lock);
	if (ret)
		goto out_put_keys;

	/*
	 * In order for us to be here, we know our q.key == key2, and since
	 * we took the hb->lock above, we also know that futex_requeue() has
	 * completed and we no longer have to concern ourselves with a wakeup
	 * race with the atomic proxy lock acquisition by the requeue code. The
	 * futex_requeue dropped our key1 reference and incremented our key2
	 * reference count.
	 */

	/* Check if the requeue code acquired the second futex for us. */
	if (!q.rt_waiter) {
		/*
		 * Got the lock. We might not be the anticipated owner if we
		 * did a lock-steal - fix up the PI-state in that case.
		 */
		if (q.pi_state && (q.pi_state->owner != current)) {
			spin_lock(q.lock_ptr);
			ret = fixup_pi_state_owner(uaddr2, &q, current);
			if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
				pi_state = q.pi_state;
				get_pi_state(pi_state);
			}
			/*
			 * Drop the reference to the pi state which
			 * the requeue_pi() code acquired for us.
			 */
			put_pi_state(q.pi_state);
			spin_unlock(q.lock_ptr);
		}
	} else {
		struct rt_mutex *pi_mutex;

		/*
		 * We have been woken up by futex_unlock_pi(), a timeout, or a
		 * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
		 * the pi_state.
		 */
		WARN_ON(!q.pi_state);
		pi_mutex = &q.pi_state->pi_mutex;
		ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);

		spin_lock(q.lock_ptr);
		if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
			ret = 0;

		debug_rt_mutex_free_waiter(&rt_waiter);
		/*
		 * Fixup the pi_state owner and possibly acquire the lock if we
		 * haven't already.
		 */
		res = fixup_owner(uaddr2, &q, !ret);
		/*
		 * If fixup_owner() returned an error, proprogate that.  If it
		 * acquired the lock, clear -ETIMEDOUT or -EINTR.
		 */
		if (res)
			ret = (res < 0) ? res : 0;

		/*
		 * If fixup_pi_state_owner() faulted and was unable to handle
		 * the fault, unlock the rt_mutex and return the fault to
		 * userspace.
		 */
		if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
			pi_state = q.pi_state;
			get_pi_state(pi_state);
		}

		/* Unqueue and drop the lock. */
		unqueue_me_pi(&q);
	}

	if (pi_state) {
		rt_mutex_futex_unlock(&pi_state->pi_mutex);
		put_pi_state(pi_state);
	}

	if (ret == -EINTR) {
		/*
		 * We've already been requeued, but cannot restart by calling
		 * futex_lock_pi() directly. We could restart this syscall, but
		 * it would detect that the user space "val" changed and return
		 * -EWOULDBLOCK.  Save the overhead of the restart and return
		 * -EWOULDBLOCK directly.
		 */
		ret = -EWOULDBLOCK;
	}

out_put_keys:
	put_futex_key(&q.key);
out_key2:
	put_futex_key(&key2);

out:
	if (to) {
		hrtimer_cancel(&to->timer);
		destroy_hrtimer_on_stack(&to->timer);
	}
	return ret;
}

Project: linux
File: futex.c

get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
	unsigned long address = (unsigned long)uaddr;
	struct mm_struct *mm = current->mm;
	struct page *page, *tail;
	struct address_space *mapping;
	int err, ro = 0;

	/*
	 * The futex address must be "naturally" aligned.
	 */
	key->both.offset = address % PAGE_SIZE;
	if (unlikely((address % sizeof(u32)) != 0))
		return -EINVAL;
	address -= key->both.offset;

	if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
		return -EFAULT;

	if (unlikely(should_fail_futex(fshared)))
		return -EFAULT;

	/*
	 * PROCESS_PRIVATE futexes are fast.
	 * As the mm cannot disappear under us and the 'key' only needs
	 * virtual address, we dont even have to find the underlying vma.
	 * Note : We do have to check 'uaddr' is a valid user address,
	 *        but access_ok() should be faster than find_vma()
	 */
	if (!fshared) {
		key->private.mm = mm;
		key->private.address = address;
		get_futex_key_refs(key);  /* implies smp_mb(); (B) */
		return 0;
	}

again:
	/* Ignore any VERIFY_READ mapping (futex common case) */
	if (unlikely(should_fail_futex(fshared)))
		return -EFAULT;

	err = get_user_pages_fast(address, 1, 1, &page);
	/*
	 * If write access is not required (eg. FUTEX_WAIT), try
	 * and get read-only access.
	 */
	if (err == -EFAULT && rw == VERIFY_READ) {
		err = get_user_pages_fast(address, 1, 0, &page);
		ro = 1;
	}
	if (err < 0)
		return err;
	else
		err = 0;

	/*
	 * The treatment of mapping from this point on is critical. The page
	 * lock protects many things but in this context the page lock
	 * stabilizes mapping, prevents inode freeing in the shared
	 * file-backed region case and guards against movement to swap cache.
	 *
	 * Strictly speaking the page lock is not needed in all cases being
	 * considered here and page lock forces unnecessarily serialization
	 * From this point on, mapping will be re-verified if necessary and
	 * page lock will be acquired only if it is unavoidable
	 *
	 * Mapping checks require the head page for any compound page so the
	 * head page and mapping is looked up now. For anonymous pages, it
	 * does not matter if the page splits in the future as the key is
	 * based on the address. For filesystem-backed pages, the tail is
	 * required as the index of the page determines the key. For
	 * base pages, there is no tail page and tail == page.
	 */
	tail = page;
	page = compound_head(page);
	mapping = READ_ONCE(page->mapping);

	/*
	 * If page->mapping is NULL, then it cannot be a PageAnon
	 * page; but it might be the ZERO_PAGE or in the gate area or
	 * in a special mapping (all cases which we are happy to fail);
	 * or it may have been a good file page when get_user_pages_fast
	 * found it, but truncated or holepunched or subjected to
	 * invalidate_complete_page2 before we got the page lock (also
	 * cases which we are happy to fail).  And we hold a reference,
	 * so refcount care in invalidate_complete_page's remove_mapping
	 * prevents drop_caches from setting mapping to NULL beneath us.
	 *
	 * The case we do have to guard against is when memory pressure made
	 * shmem_writepage move it from filecache to swapcache beneath us:
	 * an unlikely race, but we do need to retry for page->mapping.
	 */
	if (unlikely(!mapping)) {
		int shmem_swizzled;

		/*
		 * Page lock is required to identify which special case above
		 * applies. If this is really a shmem page then the page lock
		 * will prevent unexpected transitions.
		 */
		lock_page(page);
		shmem_swizzled = PageSwapCache(page) || page->mapping;
		unlock_page(page);
		put_page(page);

		if (shmem_swizzled)
			goto again;

		return -EFAULT;
	}

	/*
	 * Private mappings are handled in a simple way.
	 *
	 * If the futex key is stored on an anonymous page, then the associated
	 * object is the mm which is implicitly pinned by the calling process.
	 *
	 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
	 * it's a read-only handle, it's expected that futexes attach to
	 * the object not the particular process.
	 */
	if (PageAnon(page)) {
		/*
		 * A RO anonymous page will never change and thus doesn't make
		 * sense for futex operations.
		 */
		if (unlikely(should_fail_futex(fshared)) || ro) {
			err = -EFAULT;
			goto out;
		}

		key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
		key->private.mm = mm;
		key->private.address = address;

		get_futex_key_refs(key); /* implies smp_mb(); (B) */

	} else {
		struct inode *inode;

		/*
		 * The associated futex object in this case is the inode and
		 * the page->mapping must be traversed. Ordinarily this should
		 * be stabilised under page lock but it's not strictly
		 * necessary in this case as we just want to pin the inode, not
		 * update the radix tree or anything like that.
		 *
		 * The RCU read lock is taken as the inode is finally freed
		 * under RCU. If the mapping still matches expectations then the
		 * mapping->host can be safely accessed as being a valid inode.
		 */
		rcu_read_lock();

		if (READ_ONCE(page->mapping) != mapping) {
			rcu_read_unlock();
			put_page(page);

			goto again;
		}

		inode = READ_ONCE(mapping->host);
		if (!inode) {
			rcu_read_unlock();
			put_page(page);

			goto again;
		}

		/*
		 * Take a reference unless it is about to be freed. Previously
		 * this reference was taken by ihold under the page lock
		 * pinning the inode in place so i_lock was unnecessary. The
		 * only way for this check to fail is if the inode was
		 * truncated in parallel which is almost certainly an
		 * application bug. In such a case, just retry.
		 *
		 * We are not calling into get_futex_key_refs() in file-backed
		 * cases, therefore a successful atomic_inc return below will
		 * guarantee that get_futex_key() will still imply smp_mb(); (B).
		 */
		if (!atomic_inc_not_zero(&inode->i_count)) {
			rcu_read_unlock();
			put_page(page);

			goto again;
		}

		/* Should be impossible but lets be paranoid for now */
		if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
			err = -EFAULT;
			rcu_read_unlock();
			iput(inode);

			goto out;
		}

		key->both.offset |= FUT_OFF_INODE; /* inode-based key */
		key->shared.inode = inode;
		key->shared.pgoff = basepage_index(tail);
		rcu_read_unlock();
	}

out:
	put_page(page);
	return err;
}

Project: linux
File: futex.c

static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
{
	u32 uninitialized_var(curval);

	if (unlikely(should_fail_futex(true)))
		return -EFAULT;

	if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
		return -EFAULT;

	/* If user space value changed, let the caller retry */
	return curval != uval ? -EAGAIN : 0;
}