CVE-2024-46847

In the Linux kernel, the following vulnerability has been resolved:

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.