138 lines
8.5 KiB
JSON
138 lines
8.5 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2025-39941",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2025-04-16T07:20:57.148Z",
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"datePublished": "2025-10-04T07:31:04.080Z",
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"dateUpdated": "2026-08-05T12:06:15.944Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-08-05T12:06:15.944Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nzram: fix slot write race condition\n\nParallel concurrent writes to the same zram index result in leaked\nzsmalloc handles. Schematically we can have something like this:\n\nCPU0 CPU1\nzram_slot_lock()\nzs_free(handle)\nzram_slot_lock()\n\t\t\t\tzram_slot_lock()\n\t\t\t\tzs_free(handle)\n\t\t\t\tzram_slot_lock()\n\ncompress\t\t\tcompress\nhandle = zs_malloc()\t\thandle = zs_malloc()\nzram_slot_lock\nzram_set_handle(handle)\nzram_slot_lock\n\t\t\t\tzram_slot_lock\n\t\t\t\tzram_set_handle(handle)\n\t\t\t\tzram_slot_lock\n\nEither CPU0 or CPU1 zsmalloc handle will leak because zs_free() is done\ntoo early. In fact, we need to reset zram entry right before we set its\nnew handle, all under the same slot lock scope."
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - The vulnerable code is the zram block-device write path (`zram_submit_bio` → `zram_write_page`), reached only through local block I/O — writes to /dev/zramN, a zram-backed filesystem, or zram swap. There is no network-facing consumer of this path.\nAC:L - The attacker controls both sides of the race: two threads issuing overlapping O_DIRECT or sub-page writes to the same 4 KiB index in a loop, with the window widened by the compress/zs_malloc stage and further by `zram_bvec_write_partial()`'s read-modify-write. The reporter reproduced it with an ordinary fio/blktests workload, and no attacker-uncontrollable condition is involved.\nPR:L - No capability check exists on the write path; the attacker only needs write access to a zram-backed device or filesystem, which unprivileged users routinely have on the dominant zram deployments (Android/ChromeOS swap, systemd zram-generator, embedded/automotive zram-backed /tmp, /var, or overlay upper dirs), or via membership in the `disk` group. Real root in the init namespace is not required.\nUI:N - The attacker's own two threads create and win the race entirely on their own. No victim action, mount, or file-open by another user is needed.\nS:U - The corruption is confined to the zram driver's slot table and zsmalloc pool within the kernel's own security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - The flag/handle desync yields two distinct kernel-memory disclosures into userspace-readable pages: a sticky ZRAM_SAME slot holding a real handle fills a whole 4 KiB page with a raw kernel heap pointer, and a sticky ZRAM_HUGE slot holding a small compressed object makes `read_incompressible_page()` `copy_page()` up to ~4 KiB of adjacent kernel memory past the end of the zspage.\nI:H - The race corrupts kernel slot metadata (handle, ZRAM_SAME/ZRAM_HUGE flags, obj_size) and the pool accounting counters, so stored page contents are silently replaced by kernel pointers or out-of-bounds heap data — corrupting file blocks or swapped-out anonymous pages belonging to other, potentially privileged, processes.\nA:H - `zs_obj_read_begin(pool, handle, NULL)` on a desynced ZRAM_HUGE slot whose object spans two zpdescs memcpys into a NULL `local_copy`, producing a kernel oops, alongside `WARN_ON` splats on decompression failure. Additionally, every won race permanently orphans a zsmalloc handle, an unbounded and repeatable leak that exhausts memory on the very device backing system swap."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"drivers/block/zram/zram_drv.c"
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],
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"versions": [
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{
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"version": "71268035f5d734ad6373d953298bd5779985497a",
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"lessThan": "ff750e9f2c4d63854c33967d1646b5e89a9a19a2",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "71268035f5d734ad6373d953298bd5779985497a",
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"lessThan": "ce4be9e4307c5a60701ff6e0cafa74caffdc54ce",
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"status": "affected",
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"versionType": "git"
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"drivers/block/zram/zram_drv.c"
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],
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"versions": [
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{
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"version": "6.14",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "6.14",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.16.9",
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"lessThanOrEqual": "6.16.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.17",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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{
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"nodes": [
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{
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"operator": "OR",
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"negate": false,
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"cpeMatch": [
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.14",
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"versionEndExcluding": "6.16.9"
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},
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.14",
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"versionEndExcluding": "6.17"
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}
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]
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}
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]
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}
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],
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/ff750e9f2c4d63854c33967d1646b5e89a9a19a2"
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},
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{
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"url": "https://git.kernel.org/stable/c/ce4be9e4307c5a60701ff6e0cafa74caffdc54ce"
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}
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],
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"title": "zram: fix slot write race condition",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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}
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} |