CVE-2024-26960
mm: swap: fix race between free_swap_and_cache() and swapoff()
Severity Score
Exploit Likelihood
Affected Versions
Public Exploits
0Exploited in Wild
-Decision
Descriptions
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<-----
En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: mm: swap: corrige la ejecución entre free_swap_and_cache() y swapoff() Anteriormente existía una ventana teórica donde swapoff() podía ejecutar y desmantelar un swap_info_struct mientras se realizaba una llamada a free_swap_and_cache(). corriendo en otro hilo. Esto podría causar, entre otras malas posibilidades, que swap_page_trans_huge_swapped() (llamado por free_swap_and_cache()) acceda a la memoria liberada para swap_map. Este es un problema teórico y no he podido provocarlo a partir de un caso de prueba. Pero ha habido un acuerdo basado en la revisión del código de que esto es posible (ver enlace a continuación). Solucionarlo usando get_swap_device()/put_swap_device(), lo que detendrá swapoff(). Hubo una verificación adicional en _swap_info_get() para confirmar que la entrada de intercambio no era gratuita. Esto no está presente en get_swap_device() porque en general no tiene sentido debido a la ejecución entre obtener la referencia y el intercambio. Así que agregué una verificación equivalente directamente en free_swap_and_cache(). Detalles de cómo provocar un posible problema (gracias a David Hildenbrand por derivar esto): --8<----- __swap_entry_free() podría ser el último usuario y dar como resultado "count == SWAP_HAS_CACHE". swapoff->try_to_unuse() se detendrá tan pronto como si->inuse_pages==0. Entonces la pregunta es: ¿alguien podría reclamar la publicación y activar si->inuse_pages==0, antes de que completemos swap_page_trans_huge_swapped()? Imagine lo siguiente: folio de 2 MiB en el swapcache. Sólo 2 subpáginas siguen siendo referencias mediante entradas de intercambio. El proceso 1 todavía hace referencia a la subpágina 0 mediante la entrada de intercambio. El proceso 2 todavía hace referencia a la subpágina 1 mediante la entrada de intercambio. El proceso 1 se cierra. Llama a free_swap_and_cache(). -> count == SWAP_HAS_CACHE [luego, adelantado en el hipervisor, etc.] El proceso 2 se cierra. Llama a free_swap_and_cache(). -> count == SWAP_HAS_CACHE El proceso 2 continúa, pasa swap_page_trans_huge_swapped() y llama a __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); ¿Qué impide que el intercambio tenga éxito después de que el proceso 2 recuperó el caché de intercambio pero antes de que el proceso 1 terminara su llamada a swap_page_trans_huge_swapped()? --8<-----
CVSS Scores
SSVC
- Decision:Track
Timeline
- 2024-02-19 CVE Reserved
- 2024-05-01 CVE Published
- 2024-05-01 EPSS Updated
- 2024-12-19 CVE Updated
- ---------- Exploited in Wild
- ---------- KEV Due Date
- ---------- First Exploit
CWE
- CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CAPEC
References (11)
URL | Tag | Source |
---|---|---|
https://git.kernel.org/stable/c/7c00bafee87c7bac7ed9eced7c161f8e5332cb4e | Vuln. Introduced | |
https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html |
URL | Date | SRC |
---|
URL | Date | SRC |
---|---|---|
https://access.redhat.com/security/cve/CVE-2024-26960 | 2024-11-12 | |
https://bugzilla.redhat.com/show_bug.cgi?id=2278178 | 2024-11-12 |
Affected Vendors, Products, and Versions
Vendor | Product | Version | Other | Status | ||||||
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Vendor | Product | Version | Other | Status | <-- --> | Vendor | Product | Version | Other | Status |
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.10.215 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.10.215" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.15.154 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.15.154" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 6.1.84 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 6.1.84" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 6.6.24 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 6.6.24" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 6.7.12 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 6.7.12" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 6.8.3 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 6.8.3" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 6.9 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 6.9" | en |
Affected
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