CVE-2024-26960 Affecting kernel-rt-trace-devel package, versions *


Severity

low

    Threat Intelligence

    EPSS
    0.04% (11th percentile)

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  • Snyk ID SNYK-CENTOS7-KERNELRTTRACEDEVEL-6799710
  • published 2 May 2024
  • disclosed 1 May 2024

How to fix?

There is no fixed version for Centos:7 kernel-rt-trace-devel.

NVD Description

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

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

mm: swap: fix race between free_swap_and_cache() and swapoff()

There was previously a theoretical window where swapoff() could run and teardown a swap_info_struct while a call to free_swap_and_cache() was running in another thread. This could cause, amongst other bad possibilities, swap_page_trans_huge_swapped() (called by free_swap_and_cache()) to access the freed memory for swap_map.

This is a theoretical problem and I haven't been able to provoke it from a test case. But there has been agreement based on code review that this is possible (see link below).

Fix it by using get_swap_device()/put_swap_device(), which will stall swapoff(). There was an extra check in _swap_info_get() to confirm that the swap entry was not free. This isn't present in get_swap_device() because it doesn't make sense in general due to the race between getting the reference and swapoff. So I've added an equivalent check directly in free_swap_and_cache().

Details of how to provoke one possible issue (thanks to David Hildenbrand for deriving this):

--8<-----

__swap_entry_free() might be the last user and result in "count == SWAP_HAS_CACHE".

swapoff->try_to_unuse() will stop as soon as soon as si->inuse_pages==0.

So the question is: could someone reclaim the folio and turn si->inuse_pages==0, before we completed swap_page_trans_huge_swapped().

Imagine the following: 2 MiB folio in the swapcache. Only 2 subpages are still references by swap entries.

Process 1 still references subpage 0 via swap entry. Process 2 still references subpage 1 via swap entry.

Process 1 quits. Calls free_swap_and_cache(). -> count == SWAP_HAS_CACHE [then, preempted in the hypervisor etc.]

Process 2 quits. Calls free_swap_and_cache(). -> count == SWAP_HAS_CACHE

Process 2 goes ahead, passes swap_page_trans_huge_swapped(), and calls __try_to_reclaim_swap().

__try_to_reclaim_swap()->folio_free_swap()->delete_from_swap_cache()-> put_swap_folio()->free_swap_slot()->swapcache_free_entries()-> swap_entry_free()->swap_range_free()-> ... WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries);

What stops swapoff to succeed after process 2 reclaimed the swap cache but before process1 finished its call to swap_page_trans_huge_swapped()?

--8<-----

CVSS Scores

version 3.1
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Snyk

5.5 low
  • Attack Vector (AV)
    Local
  • Attack Complexity (AC)
    Low
  • Privileges Required (PR)
    Low
  • User Interaction (UI)
    None
  • Scope (S)
    Unchanged
  • Confidentiality (C)
    None
  • Integrity (I)
    None
  • Availability (A)
    High
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Red Hat

5.5 medium
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SUSE

5.5 medium