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Date:   Tue, 18 Oct 2022 03:15:36 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Gunthorpe <jgg@ziepe.ca>, Nishanth Menon <nm@ti.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Won Chung <wonchung@google.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] driver core: Add __alloc_size hint to devm allocators
Message-ID: <202210180310.A13EAA7@keescook>
References: <20221018073430.never.551-kees@kernel.org>
 <d199c2af-06af-8a50-a6a1-00eefa0b67b4@prevas.dk>
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On Tue, Oct 18, 2022 at 12:09:30PM +0200, Rasmus Villemoes wrote:
> On 18/10/2022 09.34, Kees Cook wrote:
> > Mark the devm_*alloc()-family of allocations with appropriate
> > __alloc_size() hints so the compiler can attempt to reason about buffer
> > lengths from allocations.
> > 
> 
> > @@ -226,7 +226,8 @@ static inline void *devm_kcalloc(struct device *dev,
> >  void devm_kfree(struct device *dev, const void *p);
> >  char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
> >  const char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp);
> > -void *devm_kmemdup(struct device *dev, const void *src, size_t len, gfp_t gfp);
> > +void *devm_kmemdup(struct device *dev, const void *src, size_t len, gfp_t gfp)
> > +	__alloc_size(3);
> 
> I think it's wrong to apply the __malloc attribute to kmemdup() and
> variants.
>
> 'malloc'
>      This tells the compiler that a function is 'malloc'-like, i.e.,
>      that the pointer P returned by the function cannot alias any other
>      pointer valid when the function returns, and moreover no pointers
>      to valid objects occur in any storage addressed by P.

Oh, ew, it defines rules about _contents_ as well. Thank you for
pointing that out!

I suppose we can use __realloc_size for these cases then?

-- 
Kees Cook