[PATCH 1/2] net/mlx4: fix build error from usercopy size check

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

The array_size() helper is used here to prevent accidental overflow in
mlx4_init_user_cqes(), but as this returns SIZE_MAX in case an overflow
would happen, the logic in copy_to_user() now detects that as overflowing
the source:

In file included from arch/x86/include/asm/preempt.h:9,
                 from include/linux/preempt.h:78,
                 from include/linux/percpu.h:6,
                 from include/linux/context_tracking_state.h:5,
                 from include/linux/hardirq.h:5,
                 from drivers/net/ethernet/mellanox/mlx4/cq.c:37:
In function 'check_copy_size',
    inlined from 'copy_to_user' at include/linux/uaccess.h:190:6,
    inlined from 'mlx4_init_user_cqes' at drivers/net/ethernet/mellanox/mlx4/cq.c:317:9,
    inlined from 'mlx4_cq_alloc' at drivers/net/ethernet/mellanox/mlx4/cq.c:394:10:
include/linux/thread_info.h:244:4: error: call to '__bad_copy_from' declared with attribute error: copy source size is too small
  244 |    __bad_copy_from();
      |    ^~~~~~~~~~~~~~~~~

Move the size logic out, and instead use the same size value for the
comparison and the copy.

Fixes: f69bf5dee7ef ("net/mlx4: Use array_size() helper in copy_to_user()")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx4/cq.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/cq.c b/drivers/net/ethernet/mellanox/mlx4/cq.c
index 4d4f9cf9facb..020cb8e2883f 100644
--- a/drivers/net/ethernet/mellanox/mlx4/cq.c
+++ b/drivers/net/ethernet/mellanox/mlx4/cq.c
@@ -290,6 +290,7 @@ static void mlx4_cq_free_icm(struct mlx4_dev *dev, int cqn)
 static int mlx4_init_user_cqes(void *buf, int entries, int cqe_size)
 {
 	int entries_per_copy = PAGE_SIZE / cqe_size;
+	size_t copy_size = array_size(entries, cqe_size);
 	void *init_ents;
 	int err = 0;
 	int i;
@@ -304,7 +305,7 @@ static int mlx4_init_user_cqes(void *buf, int entries, int cqe_size)
 	 */
 	memset(init_ents, 0xcc, PAGE_SIZE);
 
-	if (entries_per_copy < entries) {
+	if (copy_size > PAGE_SIZE) {
 		for (i = 0; i < entries / entries_per_copy; i++) {
 			err = copy_to_user((void __user *)buf, init_ents, PAGE_SIZE) ?
 				-EFAULT : 0;
@@ -315,7 +316,7 @@ static int mlx4_init_user_cqes(void *buf, int entries, int cqe_size)
 		}
 	} else {
 		err = copy_to_user((void __user *)buf, init_ents,
-				   array_size(entries, cqe_size)) ?
+				   copy_size) ?
 			-EFAULT : 0;
 	}
 
-- 
2.39.2