Re: [PATCH v3 3/4] devres: provide devm_kstrdup_const()

[Bartosz Golaszewski]

czw., 27 wrz 2018 o 01:20 Kees Cook <keescook@xxxxxxxxxxxx> napisaÅ(a):
>
> On Mon, Sep 24, 2018 at 3:11 AM, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> > Provide a resource managed version of kstrdup_const(). This variant
> > internally calls devm_kstrdup() on pointers that are outside of
> > .rodata section and returns the string as is otherwise.
> >
> > Also provide a corresponding version of devm_kfree().
> >
> > Signed-off-by: Bartosz Golaszewski <brgl@xxxxxxxx>
> > Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> > ---
> >  drivers/base/devres.c  | 38 ++++++++++++++++++++++++++++++++++++++
> >  include/linux/device.h |  3 +++
> >  2 files changed, 41 insertions(+)
> >
> > diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> > index 438c91a43508..48185d57bc5b 100644
> > --- a/drivers/base/devres.c
> > +++ b/drivers/base/devres.c
> > @@ -11,6 +11,8 @@
> >  #include <linux/slab.h>
> >  #include <linux/percpu.h>
> >
> > +#include <asm/sections.h>
> > +
> >  #include "base.h"
> >
> >  struct devres_node {
> > @@ -822,6 +824,28 @@ char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp)
> >  }
> >  EXPORT_SYMBOL_GPL(devm_kstrdup);
> >
> > +/**
> > + * devm_kstrdup_const - resource managed conditional string duplication
> > + * @dev: device for which to duplicate the string
> > + * @s: the string to duplicate
> > + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> > + *
> > + * Strings allocated by devm_kstrdup_const will be automatically freed when
> > + * the associated device is detached.
> > + *
> > + * RETURNS:
> > + * Source string if it is in .rodata section otherwise it falls back to
> > + * devm_kstrdup.
> > + */
> > +const char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
> > +{
> > +       if (is_kernel_rodata((unsigned long)s))
> > +               return s;
> > +
> > +       return devm_kstrdup(dev, s, gfp);
> > +}
> > +EXPORT_SYMBOL(devm_kstrdup_const);
> > +
> >  /**
> >   * devm_kvasprintf - Allocate resource managed space and format a string
> >   *                  into that.
> > @@ -895,6 +919,20 @@ void devm_kfree(struct device *dev, const void *p)
> >  }
> >  EXPORT_SYMBOL_GPL(devm_kfree);
> >
> > +/**
> > + * devm_kfree_const - Resource managed conditional kfree
> > + * @dev: device this memory belongs to
> > + * @p: memory to free
> > + *
> > + * Function calls devm_kfree only if @p is not in .rodata section.
> > + */
> > +void devm_kfree_const(struct device *dev, const void *p)
> > +{
> > +       if (!is_kernel_rodata((unsigned long)p))
> > +               devm_kfree(dev, p);
> > +}
> > +EXPORT_SYMBOL(devm_kfree_const);
> > +
> >  /**
> >   * devm_kmemdup - Resource-managed kmemdup
> >   * @dev: Device this memory belongs to
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 33f7cb271fbb..79ccc6eb0975 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -693,7 +693,10 @@ static inline void *devm_kcalloc(struct device *dev,
> >         return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
> >  }
> >  extern void devm_kfree(struct device *dev, const void *p);
> > +extern void devm_kfree_const(struct device *dev, const void *p);
>
> With devm_kfree and devm_kfree_const both taking "const", how are
> devm_kstrdup_const() and devm_kfree_const() going to be correctly
> paired at compile time? (i.e. I wasn't expecting the prototype change
> to devm_kfree())
>

I guess the same as with kfree() and kfree_const() which both take
const void * as argument - it's up to users to only use
devm_kfree_const() on resources allocated with devm_kstrdup_const().

Bart

> -Kees
>
> >  extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
> > +extern const char *devm_kstrdup_const(struct device *dev,
> > +                                     const char *s, gfp_t gfp);
> >  extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
> >                           gfp_t gfp);
> >
> > --
> > 2.18.0
> >
>
>
>
> --
> Kees Cook
> Pixel Security