[PATCH v2 0/5] mm/slub: Improve data handling of krealloc() when orig_size is enabled

[Feng Tang]

Danilo Krummrich's patch [1] raised one problem about krealloc() that
its caller doesn't pass the old request size, say the object is 64
bytes kmalloc one, but caller originally only requested 48 bytes. Then
when krealloc() shrinks or grows in the same object, or allocate a new
bigger object, it lacks this 'original size' information to do accurate
data preserving or zeroing (when __GFP_ZERO is set).

Thus with slub debug redzone and object tracking enabled, parts of the
object after krealloc() might contain redzone data instead of zeroes,
which is violating the __GFP_ZERO guarantees. Good thing is in this
case, kmalloc caches do have this 'orig_size' feature, which could be
used to improve the situation here.

To make the 'orig_size' accurate, we adjust some kasan/slub meta data
handling. Also add a slub kunit test case for krealloc().

This patchset has dependency over patches in both -mm tree and -slab
trees, so it is written based on linux-next tree '20240910' version.

[1]. https://lore.kernel.org/lkml/20240812223707.32049-1-dakr@xxxxxxxxxx/

Thanks,
Feng

Changelog:

  Since v1:
  * Drop the patch changing generic kunit code from this patchset,
    and will send it separately.
  * Separate the krealloc moving form slab_common.c to slub.c to a 
    new patch for better review (Danilo/Vlastimil)
  * Improve commit log and comments (Vlastimil/Danilo) 
  * Rework the kunit test case to remove its dependency over
    slub_debug (which is incomplete in v1) (Vlastimil)
  * Add ack and review tag from developers.

Feng Tang (5):
  mm/kasan: Don't store metadata inside kmalloc object when
    slub_debug_orig_size is on
  mm/slub: Consider kfence case for get_orig_size()
  mm/slub: Move krealloc() and related code to slub.c
  mm/slub: Improve redzone check and zeroing for krealloc()
  mm/slub, kunit: Add testcase for krealloc redzone and zeroing

 lib/slub_kunit.c   |  42 +++++++++++++++
 mm/kasan/generic.c |   7 ++-
 mm/slab.h          |   6 +++
 mm/slab_common.c   |  84 ------------------------------
 mm/slub.c          | 125 ++++++++++++++++++++++++++++++++++++++-------
 5 files changed, 160 insertions(+), 104 deletions(-)

-- 
2.34.1