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.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Danilo Krummrich <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Hyeonggon Yoo <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions