From: David Laight <david.laight.linux@gmail•com>
To: Andy Shevchenko <andriy.shevchenko@linux•intel.com>
Cc: "Kees Cook" <kees@kernel•org>,
"Luis Chamberlain" <mcgrof@kernel•org>,
"Pengpeng Hou" <pengpeng@iscas•ac.cn>,
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Subject: Re: [PATCH 01/11] params: bound array element output to the caller's page buffer
Date: Tue, 2 Jun 2026 14:04:51 +0100 [thread overview]
Message-ID: <20260602140451.2e3e6622@pumpkin> (raw)
In-Reply-To: <ah699hwLxIIOZ0-7@ashevche-desk.local>
On Tue, 2 Jun 2026 14:26:46 +0300
Andy Shevchenko <andriy.shevchenko@linux•intel.com> wrote:
> On Thu, May 21, 2026 at 06:33:14AM -0700, Kees Cook wrote:
> >
> > param_array_get() appends each element's string representation into the
> > shared sysfs page buffer by passing buffer + off to the element getter.
> >
> > That works for getters that only write a small bounded string, but
> > param_get_charp() and similar helpers format against PAGE_SIZE from the
> > pointer they receive. Once off is non-zero, an element getter can
> > therefore write past the end of the original sysfs page buffer.
> >
> > Collect each element into a temporary PAGE_SIZE buffer first and then
> > copy only the remaining space into the caller's page buffer.
>
> ...
>
> > + elem_buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
>
> get_free_page() (or how it is called)?
The kmalloc() should be faster and I think has to be aligned.
There is another patch set to replace get_free_pages() with kmalloc().
Although all these 'show' functions should really head to using a safer
interface.
Although, at the moment, it is really difficult to find the ones that
are guaranteed to be passed a page aligned buffer.
-- David
>
> > + if (!elem_buf)
> > + return -ENOMEM;
> > +
> > for (i = off = 0; i < (arr->num ? *arr->num : arr->max); i++) {
> > - /* Replace \n with comma */
> > - if (i)
> > - buffer[off - 1] = ',';
> > p.arg = arr->elem + arr->elemsize * i;
> > check_kparam_locked(p.mod);
> > - ret = arr->ops->get(buffer + off, &p);
> > + ret = arr->ops->get(elem_buf, &p);
> > if (ret < 0)
> > - return ret;
> > + goto out;
> > + ret = min(ret, (int)(PAGE_SIZE - 1 - off));
>
> It's usually discouraged to use castings in min/max/clamp. Can we make ret long
> or do something different here?
>
> > + if (!ret)
> > + break;
>
> > + /* Replace the previous element's trailing newline with a comma. */
> > + if (i)
> > + buffer[off - 1] = ',';
>
> Can't we do this after with help of strreplace()?
>
> > + memcpy(buffer + off, elem_buf, ret);
> > off += ret;
> > + if (off == PAGE_SIZE - 1)
> > + break;
> > }
> > buffer[off] = '\0';
> > - return off;
> > + ret = off;
> > +out:
> > + kfree(elem_buf);
> > + return ret;
>
next prev parent reply other threads:[~2026-06-02 13:04 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 13:33 [PATCH 00/11] Convert moduleparams to seq_buf Kees Cook
2026-05-21 13:33 ` [PATCH 01/11] params: bound array element output to the caller's page buffer Kees Cook
2026-05-21 16:46 ` David Laight
2026-06-01 20:23 ` Matthew Wilcox
2026-06-02 11:26 ` Andy Shevchenko
2026-06-02 12:33 ` Jason Gunthorpe
2026-06-02 13:04 ` David Laight [this message]
2026-05-21 13:33 ` [PATCH 02/11] panic: Replace panic_print_get() with generic helper Kees Cook
2026-05-21 13:33 ` [PATCH 03/11] moduleparam: Add DEFINE_KERNEL_PARAM_OPS macro family Kees Cook
2026-05-25 13:27 ` Petr Pavlu
2026-05-21 13:33 ` [PATCH 04/11] treewide: Convert struct kernel_param_ops initializers to DEFINE_KERNEL_PARAM_OPS Kees Cook
2026-05-21 13:59 ` Sean Christopherson
2026-05-22 17:01 ` Rafael J. Wysocki
2026-05-23 0:38 ` SeongJae Park
2026-05-25 13:35 ` Petr Pavlu
2026-05-21 13:33 ` [PATCH 05/11] moduleparam: Rename .get field to .get_str Kees Cook
2026-05-21 13:33 ` [PATCH 06/11] moduleparam: Add seq_buf-based .get callback alongside .get_str Kees Cook
2026-05-25 16:19 ` Petr Pavlu
2026-05-21 13:33 ` [PATCH 07/11] moduleparam: Route DEFINE_KERNEL_PARAM_OPS get pointer via _Generic Kees Cook
2026-05-25 16:24 ` Petr Pavlu
2026-05-21 13:33 ` [PATCH 08/11] params: Convert generic kernel_param_ops .get helpers to seq_buf Kees Cook
2026-05-25 17:10 ` Petr Pavlu
2026-05-21 13:33 ` [PATCH 09/11] treewide: Convert custom kernel_param_ops .get callbacks to seq_buf via cocci Kees Cook
2026-05-21 13:45 ` Sean Christopherson
2026-05-22 17:03 ` Rafael J. Wysocki
2026-05-23 0:45 ` SeongJae Park
2026-05-21 13:33 ` [PATCH 10/11] treewide: Manually convert custom kernel_param_ops .get callbacks Kees Cook
2026-05-21 17:44 ` Jani Nikula
2026-05-22 17:05 ` Rafael J. Wysocki
2026-05-21 13:33 ` [PATCH 11/11] moduleparam: Drop legacy kernel_param_ops .get_str field and dispatch logic Kees Cook
2026-05-26 6:53 ` [PATCH 00/11] Convert moduleparams to seq_buf Petr Pavlu
2026-06-01 19:59 ` Kees Cook
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