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<-----
References
Configurations
Configuration 1 (hide)
|
Configuration 2 (hide)
|
History
20 Mar 2025, 21:28
| Type | Values Removed | Values Added |
|---|---|---|
| CPE | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* |
|
| First Time |
Debian debian Linux
Linux linux Kernel Debian Linux |
|
| References | () https://git.kernel.org/stable/c/0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a - Patch | |
| References | () https://git.kernel.org/stable/c/1ede7f1d7eed1738d1b9333fd1e152ccb450b86a - Patch | |
| References | () https://git.kernel.org/stable/c/2da5568ee222ce0541bfe446a07998f92ed1643e - Patch | |
| References | () https://git.kernel.org/stable/c/363d17e7f7907c8e27a9e86968af0eaa2301787b - Patch | |
| References | () https://git.kernel.org/stable/c/3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39 - Patch | |
| References | () https://git.kernel.org/stable/c/82b1c07a0af603e3c47b906c8e991dc96f01688e - Patch | |
| References | () https://git.kernel.org/stable/c/d85c11c97ecf92d47a4b29e3faca714dc1f18d0d - Patch | |
| References | () https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html - Mailing List, Third Party Advisory |
Information
Published : 2024-05-01 06:15
Updated : 2025-03-20 21:28
NVD link : CVE-2024-26960
Mitre link : CVE-2024-26960
CVE.ORG link : CVE-2024-26960
JSON object : View
Products Affected
linux
- linux_kernel
debian
- debian_linux
CWE
CWE-362
Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')