The patch titled
Subject: mm: krealloc: consider spare memory for __GFP_ZERO
has been added to the -mm mm-unstable branch. Its filename is
mm-krealloc-consider-spare-memory-for-__gfp_zero.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-krealloc-consider-spare-memory-for-__gfp_zero.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Danilo Krummrich <dakr@xxxxxxxxxx>
Subject: mm: krealloc: consider spare memory for __GFP_ZERO
Date: Tue, 13 Aug 2024 00:34:34 +0200
As long as krealloc() is called with __GFP_ZERO consistently, starting
with the initial memory allocation, __GFP_ZERO should be fully honored.
However, if for an existing allocation krealloc() is called with a
decreased size, it is not ensured that the spare portion the allocation is
zeroed. Thus, if krealloc() is subsequently called with a larger size
again, __GFP_ZERO can't be fully honored, since we don't know the previous
size, but only the bucket size.
Example:
buf = kzalloc(64, GFP_KERNEL);
memset(buf, 0xff, 64);
buf = krealloc(buf, 48, GFP_KERNEL | __GFP_ZERO);
/* After this call the last 16 bytes are still 0xff. */
buf = krealloc(buf, 64, GFP_KERNEL | __GFP_ZERO);
Fix this, by explicitly setting spare memory to zero, when shrinking an
allocation with __GFP_ZERO flag set or init_on_alloc enabled.
Link: https://lkml.kernel.org/r/20240812223707.32049-1-dakr@xxxxxxxxxx
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab_common.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/mm/slab_common.c~mm-krealloc-consider-spare-memory-for-__gfp_zero
+++ a/mm/slab_common.c
@@ -1273,6 +1273,13 @@ __do_krealloc(const void *p, size_t new_
/* If the object still fits, repoison it precisely. */
if (ks >= new_size) {
+ /* Zero out spare memory. */
+ if (want_init_on_alloc(flags)) {
+ kasan_disable_current();
+ memset((void *)p + new_size, 0, ks - new_size);
+ kasan_enable_current();
+ }
+
p = kasan_krealloc((void *)p, new_size, flags);
return (void *)p;
}
_
Patches currently in -mm which might be from dakr@xxxxxxxxxx are
mm-vmalloc-implement-vrealloc.patch
mm-vmalloc-implement-vrealloc-fix.patch
mm-vmalloc-implement-vrealloc-fix-2.patch
mm-vmalloc-implement-vrealloc-fix-3.patch
mm-vmalloc-implement-vrealloc-fix-4.patch
mm-kvmalloc-align-kvrealloc-with-krealloc.patch
mm-kvmalloc-align-kvrealloc-with-krealloc-fix.patch
mm-kvmalloc-align-kvrealloc-with-krealloc-fix-2.patch
mm-kvmalloc-align-kvrealloc-with-krealloc-fix-3.patch
mm-krealloc-consider-spare-memory-for-__gfp_zero.patch
mm-krealloc-clarify-valid-usage-of-__gfp_zero.patch
