scsi: target: tcmu: Fix possible page UAF

tcmu_try_get_data_page() looks up pages under cmdr_lock, but it does not
take refcount properly and just returns page pointer. When
tcmu_try_get_data_page() returns, the returned page may have been freed by
tcmu_blocks_release().

We need to get_page() under cmdr_lock to avoid concurrent
tcmu_blocks_release().

Link: https://lore.kernel.org/r/20220311132206.24515-1-xiaoguang.wang@linux.alibaba.com
Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 95d4ca5..fd7267b 100644 (file)
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1821,6 +1821,7 @@ static struct page *tcmu_try_get_data_page(struct tcmu_dev *udev, uint32_t dpi)
        mutex_lock(&udev->cmdr_lock);
        page = xa_load(&udev->data_pages, dpi);
        if (likely(page)) {
+               get_page(page);
                mutex_unlock(&udev->cmdr_lock);
                return page;
        }
@@ -1877,6 +1878,7 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
                /* For the vmalloc()ed cmd area pages */
                addr = (void *)(unsigned long)info->mem[mi].addr + offset;
                page = vmalloc_to_page(addr);
+               get_page(page);
        } else {
                uint32_t dpi;
 
@@ -1887,7 +1889,6 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
                        return VM_FAULT_SIGBUS;
        }
 
-       get_page(page);
        vmf->page = page;
        return 0;
 }