[PATCH 4.19 14/32] scsi: target: tcmu: Fix possible page UAF

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

[ Upstream commit a6968f7a367f128d120447360734344d5a3d5336 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 dd7307375504..f29d600357f3 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1499,6 +1499,7 @@ static struct page *tcmu_try_get_block_page(struct tcmu_dev *udev, uint32_t dbi)
 	mutex_lock(&udev->cmdr_lock);
 	page = tcmu_get_block_page(udev, dbi);
 	if (likely(page)) {
+		get_page(page);
 		mutex_unlock(&udev->cmdr_lock);
 		return page;
 	}
@@ -1537,6 +1538,7 @@ 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 dbi;
 
@@ -1547,7 +1549,6 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
 			return VM_FAULT_SIGBUS;
 	}
 
-	get_page(page);
 	vmf->page = page;
 	return 0;
 }
-- 
2.35.1