[PATCH] rapidio: Avoid bogus __alloc_size warning

[Kees Cook <keescook@chromium.org>]

GCC 9.3 (but not later) incorrectly evaluates the arguments to
check_copy_size(), getting seemingly confused by the size being returned
from array_size(). Instead, perform the calculation once, which both
makes the code more readable and avoids the bug in GCC.

   In file included from arch/x86/include/asm/preempt.h:7,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:55,
                    from include/linux/mm_types.h:9,
                    from include/linux/buildid.h:5,
                    from include/linux/module.h:14,
                    from drivers/rapidio/devices/rio_mport_cdev.c:13:
   In function 'check_copy_size',
       inlined from 'copy_from_user' at include/linux/uaccess.h:191:6,
       inlined from 'rio_mport_transfer_ioctl' at drivers/rapidio/devices/rio_mport_cdev.c:983:6:
   include/linux/thread_info.h:213:4: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
     213 |    __bad_copy_to();
         |    ^~~~~~~~~~~~~~~

But the allocation size and the copy size are identical:

	transfer = vmalloc(array_size(sizeof(*transfer), transaction.count));
	if (!transfer)
		return -ENOMEM;

	if (unlikely(copy_from_user(transfer,
				    (void __user *)(uintptr_t)transaction.block,
				    array_size(sizeof(*transfer), transaction.count)))) {

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/linux-mm/202109091134.FHnRmRxu-lkp@intel.com/
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Jing Xiangfeng <jingxiangfeng@huawei.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/rapidio/devices/rio_mport_cdev.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index 94331d999d27..7df466e22282 100644
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -965,6 +965,7 @@ static int rio_mport_transfer_ioctl(struct file *filp, void __user *arg)
 	struct rio_transfer_io *transfer;
 	enum dma_data_direction dir;
 	int i, ret = 0;
+	size_t size;
 
 	if (unlikely(copy_from_user(&transaction, arg, sizeof(transaction))))
 		return -EFAULT;
@@ -976,13 +977,14 @@ static int rio_mport_transfer_ioctl(struct file *filp, void __user *arg)
 	     priv->md->properties.transfer_mode) == 0)
 		return -ENODEV;
 
-	transfer = vmalloc(array_size(sizeof(*transfer), transaction.count));
+	size = array_size(sizeof(*transfer), transaction.count);
+	transfer = vmalloc(size);
 	if (!transfer)
 		return -ENOMEM;
 
 	if (unlikely(copy_from_user(transfer,
 				    (void __user *)(uintptr_t)transaction.block,
-				    array_size(sizeof(*transfer), transaction.count)))) {
+				    size))) {
 		ret = -EFAULT;
 		goto out_free;
 	}
@@ -994,8 +996,7 @@ static int rio_mport_transfer_ioctl(struct file *filp, void __user *arg)
 			transaction.sync, dir, &transfer[i]);
 
 	if (unlikely(copy_to_user((void __user *)(uintptr_t)transaction.block,
-				  transfer,
-				  array_size(sizeof(*transfer), transaction.count))))
+				  transfer, size)))
 		ret = -EFAULT;
 
 out_free:
-- 
2.30.2