Subject: CVE-2024-46847: mm: vmalloc: ensure vmap_block is initialised before adding to queue

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2024-46847 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.6.37 with commit 88e0ad40d08a and fixed in 6.6.51 with commit 1b2770e27d6d
	Issue introduced in 6.10 with commit 8c61291fd850 and fixed in 6.10.10 with commit 6cf74e0e5e3a
	Issue introduced in 6.10 with commit 8c61291fd850 and fixed in 6.11 with commit 3e3de7947c75
	Issue introduced in 6.9.8 with commit 9983b81579be

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-46847
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	mm/vmalloc.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1b2770e27d6d952f491bb362b657e5b2713c3efd
	https://git.kernel.org/stable/c/6cf74e0e5e3ab5d5c9defb4c73dad54d52224671
	https://git.kernel.org/stable/c/3e3de7947c751509027d26b679ecd243bc9db255