mm/slab: sample slab_state once in kmem_cache_destroy()

kmem_cache_release() tests slab_state >= FULL after kmem_cache_destroy()
has dropped slab_mutex and unlinked the cache, and for a
SLAB_TYPESAFE_BY_RCU cache after rcu_barrier(). If slab_late_init() runs
before that test it sets slab_state to FULL but skips the unlinked cache,
which never got a sysfs entry, so sysfs_slab_release() calls kobject_put()
on a kobject that was never initialized:

  WARNING: lib/kobject.c:734 at kobject_put+0x64/0x2c0, CPU#1: kworker/u8:3/55
  kobject: '(null)' ((____ptrval____)): is not initialized, yet kobject_put() is being called.
  refcount_t: underflow; use-after-free.
  kobject_put+0x64/0x2c0
  sysfs_slab_release+0xc/0x20
  kmem_cache_destroy+0x104/0x1e0
  bioset_exit+0x13c/0x1e0
  disk_release+0x54/0x140
  put_disk+0x18/0x40
  floppy_async_init+0xbec/0xd10

slab_state >= FULL asks whether the cache has a kobject, which cache
creation skips while slab_state <= UP. UP is the state just below FULL,
so a false sample cannot skip a kobject_put() that was owed.

Seen on sparc64 at boot, where the asynchronous floppy init tears down
its bio slab while the late initcalls are running.

Sample slab_state once, under slab_mutex which slab_late_init() holds
when it sets FULL, and use the result for both the unlink and the
release.

The history of this problem dates back to v3.2:

  Commit 69cb8e6b7c29 ("slub: free slabs without holding locks") in
  v3.2 moved sysfs_slab_remove() outside slub_lock and introduced
  a race condition between kmem_cache_destroy() and slab_sysfs_init().

  Commit 945cf2b6199be ("mm/sl[aou]b: Extract a common function for
  kmem_cache_destroy") in v3.7 accidentally closed the race while
  extracting a common implementation for kmem_cache_destroy().

  Commit 5413dfba88d6 ("slub: drop mutex before deleting sysfs entry")
  in v3.8 re-opened the race by dropping slab_mutex around
  sysfs_slab_remove() in __kmem_cache_shutdown(), to avoid a lockdep
  splat between slab_mutex and the sysfs lock.

  Commit 657dc2f97220 ("slab: remove synchronous rcu_barrier() call in
  memcg cache release path") in v4.11 shifted from synchronous
  rcu_barrier() to asynchronous RCU work for SLAB_TYPESAFE_BY_RCU caches.
  That commit, again, accidentally closed the race by moving
  sysfs_slab_release() to shutdown_cache(), but only for
  !SLAB_TYPESAFE_BY_RCU caches because destruction of
  SLAB_TYPESAFE_BY_RCU caches is done in an RCU work.

  Commit 0495e337b703 ("mm/slab_common: Deleting kobject in
  kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock") in
  v6.0 re-introduced the race for !SLAB_TYPESAFE_BY_RCU caches.

Fixes: 69cb8e6b7c29 ("slub: free slabs without holding locks")
Fixes: 5413dfba88d6 ("slub: drop mutex before deleting sysfs entry")
Fixes: 0495e337b703 ("mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock")
Cc: stable@vger.kernel.org
Signed-off-by: Imre Kaloz <kaloz@kernel.org>
Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Reviewed-by: Harry Yoo (Meta) <harry@kernel.org>
Link: https://patch.msgid.link/20261014150844.8536-1-kaloz@kernel.org
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Harry Yoo (Meta) <harry@kernel.org>

0 files changed, 0 insertions, 0 deletions