CVE-2026-80718mm/percpu-km: fix bitmap overflow and accounting in pcpu_create_chunk()

Official description

In the Linux kernel, the following vulnerability has been resolved: mm/percpu-km: fix bitmap overflow and accounting in pcpu_create_chunk() In pcpu_create_chunk(), nr_pages is the total contiguous backing allocation, i.e., nr_units * pcpu_unit_pages, but pcpu_chunk_populated() uses it to set chunk->populated, whose size is pcpu_unit_pages, bitmap. Since bit N in chunk->populated means page offset N inside every unit is backed. When nr_units > 1, the function writes beyond chunk->populated. Fix it by using chunk->nr_pages. It also fixes the global pcpu_nr_empty_pop_pages accounting, since pcpu_balance_free() only iterates up to chunk->nr_pages. Commit a63d4ac4ab609 ("percpu: make percpu-km set chunk->populated bitmap properly") introduced the bitmap overflow issue. Later, commit b539b87fed37f ("percpu: implmeent pcpu_nr_empty_pop_pages and chunk->nr_populated") added pcpu_nr_empty_pop_pages and caused the accounting issue.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/5f43d2c1bea280dcdfabaf156c25e7402fb8039f
• https://git.kernel.org/stable/c/92c43ac3c2b09eb16162e8144e73c00b7c3e29d6
• https://git.kernel.org/stable/c/6fc7da2a052f2825fff785e860e67183f5acaaba
• https://git.kernel.org/stable/c/01504da375f5b19df195cb1cb1cf1dd184318f97
• https://git.kernel.org/stable/c/a6940b84c8c035da465b7165fdfcfb005545724e
• https://git.kernel.org/stable/c/32134cf9211b83bed9076d0739c5906fbea4c763
• https://git.kernel.org/stable/c/5c7fc39bf19abb38a996aaad77b3e3a8f48581c3
• https://git.kernel.org/stable/c/89b1b79c308818a715e75f28744b70d8940a07c9