[PATCH] firewire: core: use struct_size and flex_array_size in ioctl_add_descriptor

[Thorsten Blum <thorsten.blum@linux.dev>]

Use struct_size() to determine the memory needed for a new 'struct
descriptor_resource' and flex_array_size() to calculate the number of
bytes to copy from userspace. This removes the hardcoded size (4 bytes)
for the 'u32 data[]' entries.

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 drivers/firewire/core-cdev.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 78b10c6ef7fe..622bcbed6f1d 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -937,11 +937,12 @@ static int ioctl_add_descriptor(struct client *client, union ioctl_arg *arg)
 	if (a->length > 256)
 		return -EINVAL;
 
-	r = kmalloc(sizeof(*r) + a->length * 4, GFP_KERNEL);
+	r = kmalloc(struct_size(r, data, a->length), GFP_KERNEL);
 	if (r == NULL)
 		return -ENOMEM;
 
-	if (copy_from_user(r->data, u64_to_uptr(a->data), a->length * 4)) {
+	if (copy_from_user(r->data, u64_to_uptr(a->data),
+			   flex_array_size(r, data, a->length))) {
 		ret = -EFAULT;
 		goto failed;
 	}
-- 
2.51.0