[patch] mm, slab: initialize object alignment on cache creation

[patch] mm, slab: initialize object alignment on cache creation

[David Rientjes]

Since 4590685546a3 ("mm/sl[aou]b: Common alignment code"), the "ralign" 
automatic variable in __kmem_cache_create() may be used as uninitialized.

The proper alignment defaults to BYTES_PER_WORD and can be overridden by 
SLAB_RED_ZONE or the alignment specified by the caller.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=85031

Reported-by: Andrei Elovikov <a.elovikov@gmail.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 a.elovikov: If you respond to this email with your full name, Andrew can 
 give proper credit for reporting this issue.

 mm/slab.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2128,7 +2128,8 @@ static int __init_refok setup_cpu_cache(struct kmem_cache *cachep, gfp_t gfp)
 int
 __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
 {
-	size_t left_over, freelist_size, ralign;
+	size_t left_over, freelist_size;
+	size_t ralign = BYTES_PER_WORD;
 	gfp_t gfp;
 	int err;
 	size_t size = cachep->size;
@@ -2161,14 +2162,6 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
 		size &= ~(BYTES_PER_WORD - 1);
 	}
 
-	/*
-	 * Redzoning and user store require word alignment or possibly larger.
-	 * Note this will be overridden by architecture or caller mandated
-	 * alignment if either is greater than BYTES_PER_WORD.
-	 */
-	if (flags & SLAB_STORE_USER)
-		ralign = BYTES_PER_WORD;
-
 	if (flags & SLAB_RED_ZONE) {
 		ralign = REDZONE_ALIGN;
 		/* If redzoning, ensure that the second redzone is suitably

Re: [patch] mm, slab: initialize object alignment on cache creation

[Christoph Lameter]

On Tue, 23 Sep 2014, David Rientjes wrote:

> The proper alignment defaults to BYTES_PER_WORD and can be overridden by
> SLAB_RED_ZONE or the alignment specified by the caller.

Where does it default to BYTES_PER_WORD in __kmem_cache_create?

Re: [patch] mm, slab: initialize object alignment on cache creation

[David Rientjes]

On Tue, 23 Sep 2014, Christoph Lameter wrote:

> > The proper alignment defaults to BYTES_PER_WORD and can be overridden by
> > SLAB_RED_ZONE or the alignment specified by the caller.
> 
> Where does it default to BYTES_PER_WORD in __kmem_cache_create?
> 

Previous to commit 4590685546a3 ("mm/sl[aou]b: Common alignment code") 
which introduced this issue.

Re: [patch] mm, slab: initialize object alignment on cache creation

[Christoph Lameter]

On Tue, 23 Sep 2014, David Rientjes wrote:

> Previous to commit 4590685546a3 ("mm/sl[aou]b: Common alignment code")
> which introduced this issue.

Ah. Ok. I see and approve.

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