scsi: target: tcmu: Fix possible page UAF

stable inclusion
from stable-v5.10.112
commit aec36b98a1bbaa84bfd8299a306e4c12314af626
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5HL0X

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aec36b98a1bbaa84bfd8299a306e4c12314af626

--------------------------------

[ Upstream commit a6968f7a ]

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.comReviewed-by: NBodo Stroesser <bostroesser@gmail.com>
Signed-off-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/target/target_core_user.c

@@ -1676,6 +1676,7 @@ 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;
 	}
@@ -1714,6 +1715,7 @@ 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;
 
@@ -1724,7 +1726,6 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
 			return VM_FAULT_SIGBUS;
 	}
 
-	get_page(page);
 	vmf->page = page;
 	return 0;
 }