iommufd/selftest: Check for overflow in IOMMU_TEST_OP_ADD_RESERVED

syzkaller found it could overflow math in the test infrastructure and
cause a WARN_ON by corrupting the reserved interval tree. This only
effects test kernels with CONFIG_IOMMUFD_TEST.

Validate the user input length in the test ioctl.

Fixes: f4b20bb34c83 ("iommufd: Add kernel support for testing iommufd")
Link: https://patch.msgid.link/r/0-v1-cd99f6049ba5+51-iommufd_syz_add_resv_jgg@nvidia.com
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Yi Liu <yi.l.liu@intel.com>
Reported-by: syzbot+57fdb0cf6a0c5d1f15a2@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69368129.a70a0220.38f243.008f.GAE@google.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
index 86446e1537949af91e6db9f0287632405014e5ee..550ff36dec3a35ff334d43108e92ccce7305333f 100644 (file)
--- a/drivers/iommu/iommufd/selftest.c
+++ b/drivers/iommu/iommufd/selftest.c
@@ -1184,14 +1184,20 @@ static int iommufd_test_add_reserved(struct iommufd_ucmd *ucmd,
                                     unsigned int mockpt_id,
                                     unsigned long start, size_t length)
 {
+       unsigned long last;
        struct iommufd_ioas *ioas;
        int rc;
 
+       if (!length)
+               return -EINVAL;
+       if (check_add_overflow(start, length - 1, &last))
+               return -EOVERFLOW;
+
        ioas = iommufd_get_ioas(ucmd->ictx, mockpt_id);
        if (IS_ERR(ioas))
                return PTR_ERR(ioas);
        down_write(&ioas->iopt.iova_rwsem);
-       rc = iopt_reserve_iova(&ioas->iopt, start, start + length - 1, NULL);
+       rc = iopt_reserve_iova(&ioas->iopt, start, last, NULL);
        up_write(&ioas->iopt.iova_rwsem);
        iommufd_put_object(ucmd->ictx, &ioas->obj);
        return rc;