iommufd: Fix protection fault in iommufd_test_syz_conv_iova

Syzkaller reported the following bug:

  general protection fault, probably for non-canonical address 0xdffffc0000000038: 0000 [#1] SMP KASAN
  KASAN: null-ptr-deref in range [0x00000000000001c0-0x00000000000001c7]
  Call Trace:
   lock_acquire
   lock_acquire+0x1ce/0x4f0
   down_read+0x93/0x4a0
   iommufd_test_syz_conv_iova+0x56/0x1f0
   iommufd_test_access_rw.isra.0+0x2ec/0x390
   iommufd_test+0x1058/0x1e30
   iommufd_fops_ioctl+0x381/0x510
   vfs_ioctl
   __do_sys_ioctl
   __se_sys_ioctl
   __x64_sys_ioctl+0x170/0x1e0
   do_syscall_x64
   do_syscall_64+0x71/0x140

This is because the new iommufd_access_change_ioas() sets access->ioas to
NULL during its process, so the lock might be gone in a concurrent racing
context.

Fix this by doing the same access->ioas sanity as iommufd_access_rw() and
iommufd_access_pin_pages() functions do.

Cc: stable@vger.kernel.org
Fixes: 9227da7816dd ("iommufd: Add iommufd_access_change_ioas(_id) helpers")
Link: https://lore.kernel.org/r/3f1932acaf1dd494d404c04364d73ce8f57f3e5e.1708636627.git.nicolinc@nvidia.com
Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
index 2bfe77b..d59e199 100644 (file)
--- a/drivers/iommu/iommufd/selftest.c
+++ b/drivers/iommu/iommufd/selftest.c
@@ -63,8 +63,8 @@ enum {
  * In syzkaller mode the 64 bit IOVA is converted into an nth area and offset
  * value. This has a much smaller randomization space and syzkaller can hit it.
  */
-static unsigned long iommufd_test_syz_conv_iova(struct io_pagetable *iopt,
-                                               u64 *iova)
+static unsigned long __iommufd_test_syz_conv_iova(struct io_pagetable *iopt,
+                                                 u64 *iova)
 {
        struct syz_layout {
                __u32 nth_area;
@@ -88,6 +88,21 @@ static unsigned long iommufd_test_syz_conv_iova(struct io_pagetable *iopt,
        return 0;
 }
 
+static unsigned long iommufd_test_syz_conv_iova(struct iommufd_access *access,
+                                               u64 *iova)
+{
+       unsigned long ret;
+
+       mutex_lock(&access->ioas_lock);
+       if (!access->ioas) {
+               mutex_unlock(&access->ioas_lock);
+               return 0;
+       }
+       ret = __iommufd_test_syz_conv_iova(&access->ioas->iopt, iova);
+       mutex_unlock(&access->ioas_lock);
+       return ret;
+}
+
 void iommufd_test_syz_conv_iova_id(struct iommufd_ucmd *ucmd,
                                   unsigned int ioas_id, u64 *iova, u32 *flags)
 {
@@ -100,7 +115,7 @@ void iommufd_test_syz_conv_iova_id(struct iommufd_ucmd *ucmd,
        ioas = iommufd_get_ioas(ucmd->ictx, ioas_id);
        if (IS_ERR(ioas))
                return;
-       *iova = iommufd_test_syz_conv_iova(&ioas->iopt, iova);
+       *iova = __iommufd_test_syz_conv_iova(&ioas->iopt, iova);
        iommufd_put_object(ucmd->ictx, &ioas->obj);
 }
 
@@ -1161,7 +1176,7 @@ static int iommufd_test_access_pages(struct iommufd_ucmd *ucmd,
        }
 
        if (flags & MOCK_FLAGS_ACCESS_SYZ)
-               iova = iommufd_test_syz_conv_iova(&staccess->access->ioas->iopt,
+               iova = iommufd_test_syz_conv_iova(staccess->access,
                                        &cmd->access_pages.iova);
 
        npages = (ALIGN(iova + length, PAGE_SIZE) -
@@ -1263,8 +1278,8 @@ static int iommufd_test_access_rw(struct iommufd_ucmd *ucmd,
        }
 
        if (flags & MOCK_FLAGS_ACCESS_SYZ)
-               iova = iommufd_test_syz_conv_iova(&staccess->access->ioas->iopt,
-                                       &cmd->access_rw.iova);
+               iova = iommufd_test_syz_conv_iova(staccess->access,
+                               &cmd->access_rw.iova);
 
        rc = iommufd_access_rw(staccess->access, iova, tmp, length, flags);
        if (rc)