From 3e9a65a38706866bf93e19f5b4936465188add10 Mon Sep 17 00:00:00 2001 From: Danilo Krummrich Date: Tue, 13 Aug 2024 00:34:34 +0200 Subject: [PATCH] mm: krealloc: consider spare memory for __GFP_ZERO commit 1a83a716ec233990e1fd5b6fbb1200ade63bf450 upstream. 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@kernel.org Signed-off-by: Danilo Krummrich Acked-by: Vlastimil Babka Acked-by: David Rientjes Cc: Christoph Lameter Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Joonsoo Kim Cc: Pekka Enberg Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- 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; }