[PATCH] rapidio: Avoid bogus __alloc_size warning

Kees Cook
2021-09-09T16:14:19Z

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