[PATCH] slab: warning if total alloc size overflow

[PATCH] slab: warning if total alloc size overflow

[Yang Bai]

Before, if the total alloc size is overflow,
we just return NULL like alloc fail. But they
are two different type problems. The former looks
more like a programming problem. So add a warning
here.

Signed-off-by: Yang Bai <hamo.by@gmail.com>
---
 include/linux/slab.h |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 573c809..5865237 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -242,8 +242,10 @@ size_t ksize(const void *);
  */
 static inline void *kcalloc(size_t n, size_t size, gfp_t flags)
 {
-	if (size != 0 && n > ULONG_MAX / size)
+	if (size != 0 && n > ULONG_MAX / size) {
+		WARN(1, "Alloc memory size (%lu * %lu) overflow.", n, size);
 		return NULL;
+	}
 	return __kmalloc(n * size, flags | __GFP_ZERO);
 }
 
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1.7.9

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Re: [PATCH] slab: warning if total alloc size overflow

[Pekka Enberg]

On Tue, 14 Feb 2012, Yang Bai wrote:
> Before, if the total alloc size is overflow,
> we just return NULL like alloc fail. But they
> are two different type problems. The former looks
> more like a programming problem. So add a warning
> here.
>
> Signed-off-by: Yang Bai <hamo.by@gmail.com>
> ---
> include/linux/slab.h |    4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 573c809..5865237 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -242,8 +242,10 @@ size_t ksize(const void *);
>  */
> static inline void *kcalloc(size_t n, size_t size, gfp_t flags)
> {
> -	if (size != 0 && n > ULONG_MAX / size)
> +	if (size != 0 && n > ULONG_MAX / size) {
> +		WARN(1, "Alloc memory size (%lu * %lu) overflow.", n, size);
> 		return NULL;
> +	}
> 	return __kmalloc(n * size, flags | __GFP_ZERO);
> }

Did you check how much kernel text size increases? I'm pretty sure we'd 
need to wrap this with CONFIG_SLAB_OVERFLOW ifdef.

 			Pekka

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Re: [PATCH] slab: warning if total alloc size overflow

[Yang Bai]

On Tue, Feb 14, 2012 at 3:31 PM, Pekka Enberg <penberg@kernel.org> wrote:
> On Tue, 14 Feb 2012, Yang Bai wrote:
>
> Did you check how much kernel text size increases? I'm pretty sure we'd need
> to wrap this with CONFIG_SLAB_OVERFLOW ifdef.
>
>                        Pekka

Hi Pekka,

I did not find anything like SLAB_OVERFLOW using grep. Could you
explain it more in detail?

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Re: [PATCH] slab: warning if total alloc size overflow

[Pekka Enberg]

On Tue, 14 Feb 2012, Yang Bai wrote:
> I did not find anything like SLAB_OVERFLOW using grep. Could you
> explain it more in detail?

You should add a new config option to lib/Kconfig.debug and wrap the debug 
check with it.

 			Pekka

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Re: [PATCH] slab: warning if total alloc size overflow

[Christoph Lameter]

On Tue, 14 Feb 2012, Pekka Enberg wrote:

> Did you check how much kernel text size increases? I'm pretty sure we'd need
> to wrap this with CONFIG_SLAB_OVERFLOW ifdef.

Remove the inlining? This function is rarely called and not performance
critical.

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Re: [PATCH] slab: warning if total alloc size overflow

[Andrew Morton]

On Tue, 14 Feb 2012 15:28:19 +0800 Yang Bai <hamo.by@gmail.com> wrote:

> Before, if the total alloc size is overflow,
> we just return NULL like alloc fail. But they
> are two different type problems. The former looks
> more like a programming problem. So add a warning
> here.
> 
> Signed-off-by: Yang Bai <hamo.by@gmail.com>
> ---
>  include/linux/slab.h |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 573c809..5865237 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -242,8 +242,10 @@ size_t ksize(const void *);
>   */
>  static inline void *kcalloc(size_t n, size_t size, gfp_t flags)
>  {
> -	if (size != 0 && n > ULONG_MAX / size)
> +	if (size != 0 && n > ULONG_MAX / size) {
> +		WARN(1, "Alloc memory size (%lu * %lu) overflow.", n, size);
>  		return NULL;
> +	}
>  	return __kmalloc(n * size, flags | __GFP_ZERO);
>  }

One of the applications of kcalloc() is to prevent userspace from
causing a multiplicative overflow (and then perhaps causing an
overwrite beyond the end of the allocated memory).

With this patch, we've just handed the user a way of spamming the logs
at 1MHz.  This is bad.


Also, please let's not randomly add debug stuff in places where we've
never demonstrated a need for it.

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Re: [PATCH] slab: warning if total alloc size overflow

[Yang Bai]

On Tue, Feb 14, 2012 at 4:53 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Tue, 14 Feb 2012 15:28:19 +0800 Yang Bai <hamo.by@gmail.com> wrote:
>
>
> One of the applications of kcalloc() is to prevent userspace from
> causing a multiplicative overflow (and then perhaps causing an
> overwrite beyond the end of the allocated memory).
>
> With this patch, we've just handed the user a way of spamming the logs
> at 1MHz.  This is bad.
>
>
> Also, please let's not randomly add debug stuff in places where we've
> never demonstrated a need for it.

Ok. Please just drop this patch.

Thanks.

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Chinese Name: 白杨
Nick Name: Hamo
Homepage: http://hamobai.com/
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Re: [PATCH] slab: warning if total alloc size overflow

[Christoph Lameter]

On Tue, 14 Feb 2012, Andrew Morton wrote:

> One of the applications of kcalloc() is to prevent userspace from
> causing a multiplicative overflow (and then perhaps causing an
> overwrite beyond the end of the allocated memory).
>
> With this patch, we've just handed the user a way of spamming the logs
> at 1MHz.  This is bad.

Well there is WARN_ON_ONCE too to prevent that.

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Re: [PATCH] slab: warning if total alloc size overflow

[Christoph Lameter]

On Tue, 14 Feb 2012, Yang Bai wrote:

> Before, if the total alloc size is overflow,
> we just return NULL like alloc fail. But they
> are two different type problems. The former looks
> more like a programming problem. So add a warning
> here.

Acked-by: Christoph Lameter <cl@linux.com>

Would be better to remove kcalloc and provide a generalized array size
calculation function that does the WARN(). That would also work for all
other variants zeroed or NUMA node spec etc etc.

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