5.4-stable review patch. If anyone has any objections, please let me know.
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From: Danilo Krummrich dakr@kernel.org
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 dakr@kernel.org Acked-by: Vlastimil Babka vbabka@suse.cz Acked-by: David Rientjes rientjes@google.com Cc: Christoph Lameter cl@linux.com Cc: Hyeonggon Yoo 42.hyeyoo@gmail.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Pekka Enberg penberg@kernel.org Cc: Roman Gushchin roman.gushchin@linux.dev Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/slab_common.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -1680,6 +1680,13 @@ static __always_inline void *__do_kreall ks = ksize(p);
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; }