CVE-2026-74672
In the Linux kernel, the following vulnerability has been resolved:
mm/vmalloc: acquire init_mm lock on huge vmap to avoid ptdump UAF
Patch series "mm: fix UAF caused by race between ptdump and vmap pgtable
freeing", v6.
Kernel page table walkers fall into two broad categories - those ranges
where no exclusion is required via walk_kernel_page_table_range_lockless()
and those where exclusion is required via walk_kernel_page_table_range()
or walk_page_range_debug().
The former category is used only by arm64 arch code operating on ranges it
both wholly owns and does not concurrently write.
The latter category consists of kernel page table walkers operating on
ranges that are wholly owned (but which need exclusion against concurrent
writers).
The lock used for exclusion is the mmap lock, and for kernel ranges this
is the mmap lock on init_mm.
ptdump is a special case being both the only user of
walk_page_range_debug(), and the only case in which it walks ranges it
does not own.
This presents a problem, as page tables may be freed under ptdump. And
indeed there is a use-after-free bug in the kernel as a result, which this
series addresses.
vmap promotes page tables to huge leaf entries where possible, freeing the
lower page table when it does. It does this with no meaningful locks held
against concurrent ptdump walks.
As a result, use-after-free can currently occur. This series addresses
the issue by having the vmap huge promotion logic acquire the mmap read
lock while both setting the huge page table entry and freeing the prior
leaf page table.
The ptdump code already acquires the mmap write lock, so by doing so we
ensure that the ptdump walker only ever observes either the huge page
table entry or the existing page table entry, and nothing is freed
underneath it.
A mitigation for this issue was already applied for arm64 in commit
fa93b45fd397 ("arm64: Enable vmalloc-huge with ptdump"), which this series
has to deal with carefully.
This mitigation resolv
CSIRTS triage
- What
- A use-after-free vulnerability in vmalloc huge vmap operations due to missing init_mm lock acquisition during ptdump traversal.
- Who is affected
- Linux kernel systems using vmalloc for large mappings that perform concurrent ptdump operations.
- Urgency
- Medium severity (CVSS 5.2) with no current exploitation; patch available upstream.
- Action
- Apply Linux kernel security patch addressing init_mm lock handling in mm/vmalloc.c.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.17% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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