From: Danilo Krummrich <dakr@xxxxxxxxxx> 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@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> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/slab_common.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/mm/slab_common.c +++ b/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 stable-queue which might be from dakr@xxxxxxxxxx are queue-6.11/mm-krealloc-consider-spare-memory-for-__gfp_zero.patch
