Improper Validation of Array Index Affecting kernel-kdump-devel package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-kdump-devel package and not the kernel-kdump-devel package as distributed by RHEL. See How to fix? for RHEL:7 relevant fixed versions and status.

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.

• https://access.redhat.com/security/cve/CVE-2024-46847
• https://git.kernel.org/stable/c/1b2770e27d6d952f491bb362b657e5b2713c3efd
• https://git.kernel.org/stable/c/3e3de7947c751509027d26b679ecd243bc9db255
• https://git.kernel.org/stable/c/6cf74e0e5e3ab5d5c9defb4c73dad54d52224671