[PATCH 1/2] scsi: target: tcmu: Fix possible page UAF

[Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>]

tcmu_try_get_data_page() looks up pages under cmdr_lock, but it don't
take refcount properly and just return page pointer.

When tcmu_try_get_data_page() returns, the returned page may have been
freed by tcmu_blocks_release(), need to get_page() under cmdr_lock to
avoid concurrent tcmu_blocks_release().

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
---
 drivers/target/target_core_user.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 7b2a89a67cdb..06a5c4086551 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1820,6 +1820,7 @@ 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;
 	}
@@ -1876,6 +1877,7 @@ 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;
 
@@ -1886,7 +1888,6 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
 			return VM_FAULT_SIGBUS;
 	}
 
-	get_page(page);
 	vmf->page = page;
 	return 0;
 }
-- 
2.14.4.44.g2045bb6