Re: [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types

[Kees Cook]

On February 23, 2026 8:05:10 AM PST, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>On Fri, Feb 20, 2026 at 11:49:23PM -0800, Kees Cook wrote:
>> This is the result of running the Coccinelle script from
>> scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
>> avoid scalar types (which need careful case-by-case checking), and
>> instead replace kmalloc-family calls that allocate struct or union
>> object instances:
>> 
>> Single allocations:	kmalloc(sizeof(TYPE), ...)
>> are replaced with:	kmalloc_obj(TYPE, ...)
>> 
>> Array allocations:	kmalloc_array(COUNT, sizeof(TYPE), ...)
>> are replaced with:	kmalloc_objs(TYPE, COUNT, ...)
>> 
>> Flex array allocations:	kmalloc(struct_size(PTR, FAM, COUNT), ...)
>> are replaced with:	kmalloc_flex(*PTR, FAM, COUNT, ...)
>> 
>> (where TYPE may also be *VAR)
>> 
>> The resulting allocations no longer return "void *", instead returning
>> "TYPE *".
>> 
>> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
>> ---
>> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
>> index 37455e74d314..42f392e6add3 100644
>> --- a/arch/um/drivers/ubd_kern.c
>> +++ b/arch/um/drivers/ubd_kern.c
>> @@ -1069,20 +1069,16 @@ static int __init ubd_init(void)
>>  	if (register_blkdev(UBD_MAJOR, "ubd"))
>>  		return -1;
>>  
>> -	irq_req_buffer = kmalloc_array(UBD_REQ_BUFFER_SIZE,
>> -				       sizeof(struct io_thread_req *),
>> -				       GFP_KERNEL
>> -		);
>> +	irq_req_buffer = kmalloc_objs(struct io_thread_req *,
>> +				      UBD_REQ_BUFFER_SIZE, GFP_KERNEL);
>>  	irq_remainder = 0;
>>  
>>  	if (irq_req_buffer == NULL) {
>>  		printk(KERN_ERR "Failed to initialize ubd buffering\n");
>>  		return -ENOMEM;
>>  	}
>> -	io_req_buffer = kmalloc_array(UBD_REQ_BUFFER_SIZE,
>> -				      sizeof(struct io_thread_req *),
>> -				      GFP_KERNEL
>> -		);
>> +	io_req_buffer = kmalloc_objs(struct io_thread_req *,
>> +				     UBD_REQ_BUFFER_SIZE, GFP_KERNEL);
>
>Building um:defconfig ... failed
>--------------
>Error log:
>arch/um/drivers/ubd_kern.c: In function 'ubd_init':
>arch/um/drivers/ubd_kern.c:1072:24: error: assignment to 'struct io_thread_req * (*)[]' from incompatible pointer type 'struct io_thread_req **' [-Wincompatible-pointer-types]
> 1072 |         irq_req_buffer = kmalloc_objs(struct io_thread_req *,
>      |                        ^
>arch/um/drivers/ubd_kern.c:1080:23: error: assignment to 'struct io_thread_req * (*)[]' from incompatible pointer type 'struct io_thread_req **' [-Wincompatible-pointer-types]
> 1080 |         io_req_buffer = kmalloc_objs(struct io_thread_req *,

Thanks for finding this! I'll get these fixed up today; I missed um in my build testing. Doing these tree-wide changes is tricky without having  a sane way to get them into -next first.

-Kees

-- 
Kees Cook