* Re: [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types
@ 2026-02-23 16:05 Guenter Roeck
2026-02-23 17:48 ` Kees Cook
2026-02-23 22:23 ` Kees Cook
0 siblings, 2 replies; 3+ messages in thread
From: Guenter Roeck @ 2026-02-23 16:05 UTC (permalink / raw)
To: Kees Cook; +Cc: linux-kernel
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@kernel.org>
> ---
> 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 *,
Guenter
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types
2026-02-23 16:05 [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types Guenter Roeck
@ 2026-02-23 17:48 ` Kees Cook
2026-02-23 22:23 ` Kees Cook
1 sibling, 0 replies; 3+ messages in thread
From: Kees Cook @ 2026-02-23 17:48 UTC (permalink / raw)
To: Guenter Roeck; +Cc: linux-kernel, Nathan Chancellor
On February 23, 2026 8:05:10 AM PST, Guenter Roeck <linux@roeck-us.net> 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@kernel.org>
>> ---
>> 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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types
2026-02-23 16:05 [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types Guenter Roeck
2026-02-23 17:48 ` Kees Cook
@ 2026-02-23 22:23 ` Kees Cook
1 sibling, 0 replies; 3+ messages in thread
From: Kees Cook @ 2026-02-23 22:23 UTC (permalink / raw)
To: Guenter Roeck; +Cc: linux-kernel
On Mon, Feb 23, 2026 at 08:05:10AM -0800, Guenter Roeck 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@kernel.org>
> > ---
> > 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 *,
>
> Guenter
Proposed solution sent now:
https://lore.kernel.org/all/20260223214341.work.846-kees@kernel.org/
--
Kees Cook
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-02-23 16:05 [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types Guenter Roeck
2026-02-23 17:48 ` Kees Cook
2026-02-23 22:23 ` Kees Cook
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