mm: vmalloc: ensure vmap_block is initialised before adding to queue

Commit 8c61291fd850 ("mm: fix incorrect vbq reference in
purge_fragmented_block") extended the 'vmap_block' structure to contain a
'cpu' field which is set at allocation time to the id of the initialising
CPU.

When a new 'vmap_block' is being instantiated by new_vmap_block(), the
partially initialised structure is added to the local 'vmap_block_queue'
xarray before the 'cpu' field has been initialised.  If another CPU is
concurrently walking the xarray (e.g.  via vm_unmap_aliases()), then it
may perform an out-of-bounds access to the remote queue thanks to an
uninitialised index.

This has been observed as UBSAN errors in Android:

 | Internal error: UBSAN: array index out of bounds: 00000000f2005512 [#1] PREEMPT SMP
 |
 | Call trace:
 |  purge_fragmented_block+0x204/0x21c
 |  _vm_unmap_aliases+0x170/0x378
 |  vm_unmap_aliases+0x1c/0x28
 |  change_memory_common+0x1dc/0x26c
 |  set_memory_ro+0x18/0x24
 |  module_enable_ro+0x98/0x238
 |  do_init_module+0x1b0/0x310

Move the initialisation of 'vb->cpu' in new_vmap_block() ahead of the
addition to the xarray.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 8c61291fd850 ("mm: fix incorrect vbq reference in purge_fragmented_block")
Signed-off-by: Will Deacon <[email protected]>
Reviewed-by: Baoquan He <[email protected]>
Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
Cc: Zhaoyang Huang <[email protected]>
Cc: Hailong.Liu <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions