[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <20240812223707.32049-1-dakr@kernel.org>
Date: Tue, 13 Aug 2024 00:34:34 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: akpm@...ux-foundation.org,
cl@...ux.com,
penberg@...nel.org,
rientjes@...gle.com,
iamjoonsoo.kim@....com,
vbabka@...e.cz,
roman.gushchin@...ux.dev,
42.hyeyoo@...il.com
Cc: linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH v2 1/2] mm: krealloc: consider spare memory for __GFP_ZERO
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.
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Danilo Krummrich <dakr@...nel.org>
---
mm/slab_common.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 40b582a014b8..cff602cedf8e 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1273,6 +1273,13 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags)
/* 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;
}
base-commit: b8dbbb7fe1db26c450a9d2c3302013154b3431df
--
2.46.0
Powered by blists - more mailing lists