Описание
In the Linux kernel, the following vulnerability has been resolved:
mm/shmem, swap: fix race of truncate and swap entry split
The helper for shmem swap freeing is not handling the order of swap
entries correctly. It uses xa_cmpxchg_irq to erase the swap entry, but it
gets the entry order before that using xa_get_order without lock
protection, and it may get an outdated order value if the entry is split
or changed in other ways after the xa_get_order and before the
xa_cmpxchg_irq.
And besides, the order could grow and be larger than expected, and cause
truncation to erase data beyond the end border. For example, if the
target entry and following entries are swapped in or freed, then a large
folio was added in place and swapped out, using the same entry, the
xa_cmpxchg_irq will still succeed, it's very unlikely to happen though.
To fix that, open code the Xarray cmpxchg and put the order retrieval and
value checking in the same critical section. Also, ensure the order won't
exceed the end border, skip it if the entry goes across the border.
Skipping large swap entries crosses the end border is safe here. Shmem
truncate iterates the range twice, in the first iteration,
find_lock_entries already filtered such entries, and shmem will swapin the
entries that cross the end border and partially truncate the folio (split
the folio or at least zero part of it). So in the second loop here, if we
see a swap entry that crosses the end order, it must at least have its
content erased already.
I observed random swapoff hangs and kernel panics when stress testing
ZSWAP with shmem. After applying this patch, all problems are gone.
A race condition was found in the Linux kernel's shmem/swap handling during truncate operations. The swap entry order is retrieved without proper lock protection, allowing it to become stale before the subsequent xa_cmpxchg_irq operation. This can cause truncation to erase data beyond the intended end border or lead to swapoff hangs and kernel panics.
Отчет
This race condition requires specific timing between truncate operations and swap entry splits under ZSWAP stress. While it can cause kernel panics, it's difficult to trigger reliably and primarily affects systems using ZSWAP with shmem/tmpfs under heavy memory pressure. No data confidentiality or integrity impact beyond the crash.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 6 | kernel | Out of support scope | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Not affected |
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Дополнительная информация
Статус:
5.5 Medium
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: mm/shmem, swap: fix race of truncate and swap entry split The helper for shmem swap freeing is not handling the order of swap entries correctly. It uses xa_cmpxchg_irq to erase the swap entry, but it gets the entry order before that using xa_get_order without lock protection, and it may get an outdated order value if the entry is split or changed in other ways after the xa_get_order and before the xa_cmpxchg_irq. And besides, the order could grow and be larger than expected, and cause truncation to erase data beyond the end border. For example, if the target entry and following entries are swapped in or freed, then a large folio was added in place and swapped out, using the same entry, the xa_cmpxchg_irq will still succeed, it's very unlikely to happen though. To fix that, open code the Xarray cmpxchg and put the order retrieval and value checking in the same critical section. Also, ensure the order won't exceed ...
In the Linux kernel, the following vulnerability has been resolved: mm/shmem, swap: fix race of truncate and swap entry split The helper for shmem swap freeing is not handling the order of swap entries correctly. It uses xa_cmpxchg_irq to erase the swap entry, but it gets the entry order before that using xa_get_order without lock protection, and it may get an outdated order value if the entry is split or changed in other ways after the xa_get_order and before the xa_cmpxchg_irq. And besides, the order could grow and be larger than expected, and cause truncation to erase data beyond the end border. For example, if the target entry and following entries are swapped in or freed, then a large folio was added in place and swapped out, using the same entry, the xa_cmpxchg_irq will still succeed, it's very unlikely to happen though. To fix that, open code the Xarray cmpxchg and put the order retrieval and value checking in the same critical section. Also, ensure the order won't exceed
In the Linux kernel, the following vulnerability has been resolved: m ...
In the Linux kernel, the following vulnerability has been resolved: mm/shmem, swap: fix race of truncate and swap entry split The helper for shmem swap freeing is not handling the order of swap entries correctly. It uses xa_cmpxchg_irq to erase the swap entry, but it gets the entry order before that using xa_get_order without lock protection, and it may get an outdated order value if the entry is split or changed in other ways after the xa_get_order and before the xa_cmpxchg_irq. And besides, the order could grow and be larger than expected, and cause truncation to erase data beyond the end border. For example, if the target entry and following entries are swapped in or freed, then a large folio was added in place and swapped out, using the same entry, the xa_cmpxchg_irq will still succeed, it's very unlikely to happen though. To fix that, open code the Xarray cmpxchg and put the order retrieval and value checking in the same critical section. Also, ensure the order won't exc...
5.5 Medium
CVSS3