[PATCH] slub: slub_def.h: needs additional check for "index"

[PATCH] slub: slub_def.h: needs additional check for "index"

[Maxin John]

In slub_def.h file, the kmalloc_index() may return -1 for some special cases.
If that negative return value gets assigned to "index", it might lead to issues
later as the variable "index" is used as index to array "kmalloc_caches" in :

return kmalloc_caches[index];

Please let me know your comments.

Signed-off-by: Maxin B. John <maxin.john@gmail.com>
---
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 45ca123..3db4b33 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -211,7 +211,7 @@ static __always_inline struct kmem_cache
*kmalloc_slab(size_t size)
 {
        int index = kmalloc_index(size);

-       if (index == 0)
+       if (index <= 0)
                return NULL;

        return kmalloc_caches[index];

[PATCH] slub: slub_def.h: needs additional check for "index"

[Maxin John]

In slub_def.h file, the kmalloc_index() may return -1 for some special cases.
If that negative return value gets assigned to "index", it might lead to issues
later as the variable "index" is used as index to array "kmalloc_caches" in :

return kmalloc_caches[index];

Please let me know your comments.

Signed-off-by: Maxin B. John <maxin.john@gmail.com>
---
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 45ca123..3db4b33 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -211,7 +211,7 @@ static __always_inline struct kmem_cache
*kmalloc_slab(size_t size)
 {
        int index = kmalloc_index(size);

-       if (index == 0)
+       if (index <= 0)
                return NULL;

        return kmalloc_caches[index];

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Re: [PATCH] slub: slub_def.h: needs additional check for "index"

[Christoph Lameter]

On Fri, 6 May 2011, Maxin John wrote:

> In slub_def.h file, the kmalloc_index() may return -1 for some special cases.
> If that negative return value gets assigned to "index", it might lead to issues
> later as the variable "index" is used as index to array "kmalloc_caches" in :


The value passed to kmalloc_slab is tested before the result is used.
kmalloc_slab() only returns -1 for values > 4MB.

The size of the object is checked against SLUB_MAX size which is
significantly smaller than 4MB. 8kb by default.

So kmalloc_slab() cannot return -1 if the parameter is checked first.

Re: [PATCH] slub: slub_def.h: needs additional check for "index"

[Christoph Lameter]

On Fri, 6 May 2011, Maxin John wrote:

> In slub_def.h file, the kmalloc_index() may return -1 for some special cases.
> If that negative return value gets assigned to "index", it might lead to issues
> later as the variable "index" is used as index to array "kmalloc_caches" in :


The value passed to kmalloc_slab is tested before the result is used.
kmalloc_slab() only returns -1 for values > 4MB.

The size of the object is checked against SLUB_MAX size which is
significantly smaller than 4MB. 8kb by default.

So kmalloc_slab() cannot return -1 if the parameter is checked first.

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Re: [PATCH] slub: slub_def.h: needs additional check for "index"

[Maxin John]

Hi,

On Fri, May 6, 2011 at 9:56 PM, Christoph Lameter <cl@linux.com> wrote:
> The value passed to kmalloc_slab is tested before the result is used.
> kmalloc_slab() only returns -1 for values > 4MB.
>
> The size of the object is checked against SLUB_MAX size which is
> significantly smaller than 4MB. 8kb by default.
>
> So kmalloc_slab() cannot return -1 if the parameter is checked first.

Thank you very much for pointing it out. I think it's a lot more clear
for me now.

Best Regards,
Maxin

Re: [PATCH] slub: slub_def.h: needs additional check for "index"

[Maxin John]

Hi,

On Fri, May 6, 2011 at 9:56 PM, Christoph Lameter <cl@linux.com> wrote:
> The value passed to kmalloc_slab is tested before the result is used.
> kmalloc_slab() only returns -1 for values > 4MB.
>
> The size of the object is checked against SLUB_MAX size which is
> significantly smaller than 4MB. 8kb by default.
>
> So kmalloc_slab() cannot return -1 if the parameter is checked first.

Thank you very much for pointing it out. I think it's a lot more clear
for me now.

Best Regards,
Maxin

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