266 lines
18 KiB
JSON
266 lines
18 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-2026-98507",
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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": "2026-09-25T10:25:14.354Z",
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"datePublished": "2026-10-18T15:17:13.767Z",
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"dateUpdated": "2026-10-30T12:38:20.652Z"
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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": "2026-10-30T12:38:20.652Z"
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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\nmm/rmap: fix missing barrier between anon_vma init and vma->anon_vma publish\n\nOn arm64 server, we find that a task trying to grab the anon_vma lock\ntriggers hungtask.\n\nINFO: task main:2354726 blocked for more than 120 seconds.\n Tainted: G E 5.10.0-0021.aarch64 #1\n\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\" disables this message.\ntask:main state:D stack: 0 pid:2354726 ppid:2350673 flags:0x00000a01\nCall trace:\n __switch_to+0x7c/0xbc\n __schedule+0x3b4/0x8a0\n schedule+0x50/0xe0\n rwsem_down_write_slowpath+0x3cc/0x6cc\n down_write+0x60/0x260\n __anon_vma_prepare+0x6c/0x210\n do_anonymous_page+0x258/0x660\n handle_pte_fault+0x188/0x214\n __handle_mm_fault+0x1b0/0x380\n handle_mm_fault+0xf4/0x284\n do_page_fault+0x19c/0x494\n do_translation_fault+0xcc/0xf8\n do_mem_abort+0x48/0xac\n el0_da+0x44/0x80\n el0_sync_handler+0x88/0xb4\n el0_sync+0x160/0x180\n\nAfter analyzing the vmcore, we found the anon_vma->root->rwsem.count is\n-1. There is another anon_vma whose anon_vma->root->rwsem.count is 1, the\nanon_vma->root->rwsem.owner shows the lock is held, but the stack of the\ntask shows the task doesn't hold the anon_vma lock.\n\nAfter adding more debugging info, we found __anon_vma_prepare() reuses\nanon_vma and triggers the UAF of anon_vma->root due to missing memory\nbarrier, leading to locking and unlocking two different anon_vma->root,\nthus leading to an anon_vma will never be unlocked, and another anon_vma\ncouldn't be locked anymore.\n\nThis race requires two adjacent VMAs that are not merged but are\nanon_vma-compatible (e.g., they differ in VMA_ACCESS_FLAGS that can be\nchanged by mprotect()). Two threads fault on each VMA concurrently, both\ncalling __anon_vma_prepare() with only mmap_lock held for reading.\n\n THREAD A THREAD B\n__anon_vma_prepare __anon_vma_prepare\n find_mergeable_anon_vma() -> NULL\n anon_vma = anon_vma_alloc();\n anon_vma->root = anon_vma;\n // the two stores may be reordered\n vma->anon_vma = anon_vma;\n // finds A's anon_vma\n anon_vma = find_mergeable_anon_vma(vma);\n anon_vma_lock_write(anon_vma);\n // may still see the old root\n down_write(&anon_vma->root->rwsem);\n anon_vma_unlock_write(anon_vma);\n // see the new root, never unlock old\n up_write(&anon_vma->root->rwsem);\n\nthread A triggers page fault and calls __anon_vma_prepare() to prepare\nanon_vma for the faulting vma. __anon_vma_prepare() allocates and\ninitializes a new anon_vma, and then publishes it to the vma with a plain\nstore. anon_vma_prepare() only requires the mmap_lock to be held for\nreading, so two threads can fault on adjacent VMAs at the same time. \nWhile thread A publishes a new anon_vma, thread B could find the anon_vma\nvia find_mergeable_anon_vma() and then locks anon_vma->root->rwsem.\n\nThe store to anon_vma->root in anon_vma_alloc() and the store to\nvma->anon_vma can be reordered. The anon_vma_lock_write() and spin_lock()\nonly provide acquire semantics, which do not prevent prior stores from\nbeing reordered after them. The release semantics of the corresponding\nspin_unlock() and anon_vma_unlock_write() come too late, the store to\nvma->anon_vma is already published before they take effect. As a result,\nthread B can observe the following order:\n\n vma->anon_vma = anon_vma;\n anon_vma->root = anon_vma;\n\nThe anon_vma slab is SLAB_TYPESAFE_BY_RCU, so a newly allocated anon_vma\nmay reuse memory from a previously freed one. The constructor\n(anon_vma_ctor) does not reset anon_vma->root, and __put_anon_vma()\ndoesn't clear it either, so the old root value persists until\nanon_vma_alloc() overwrites it. If that store isn't v\n---truncated---"
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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 - A local memory fault reaches patched __anon_vma_prepare() via do_mem_abort() → do_page_fault() → handle_mm_fault() → __handle_mm_fault() → handle_pte_fault() → do_anonymous_page() → __vmf_anon_prepare(); no network data enters this path.\nAC:L - The attacker can use mprotect() to create adjacent unmerged VMAs differing in VMA_ACCESS_FLAGS, groom stale non-self roots through fork/exit, and concurrently fault both VMAs. They control both sides of the reusable_anon_vma() race and can retry the weak-memory window.\nPR:L - mmap(), mprotect(), fork()/clone(), and faults on the caller's own mappings require no capability; neither __vmf_anon_prepare() nor __anon_vma_prepare() performs a credential check. An ordinary unprivileged local process can reach the flaw.\nUI:N - The attacking process creates the VMA layout, grooms the anon_vma cache, and drives both concurrent faults itself; no action by another user is required.\nS:U - The stale root dereference and rwsem corruption occur in the host kernel's anon_vma memory-management state reached from the attacker's process; no VM, IOMMU, or other security-authority boundary is crossed.\nC:H - reusable_anon_vma() can return a newly allocated SLAB_TYPESAFE_BY_RCU object while its root still names a freed prior anon_vma, after which anon_vma_lock_write() dereferences the stale root->rwsem. Same-cache grooming therefore provides a use-after-free read over recycled kernel object state.\nI:H - down_write() writes count and owner state through the freed or reallocated old root, while anon_vma_unlock_write() rereads the initialized root and up_write() corrupts that different semaphore, as demonstrated by counts 1 and -1. These are cross-object UAF writes into a groomable kernel slab.\nA:H - The mismatched down_write()/up_write() leaves the old anon_vma root permanently locked and underflows the new root's rwsem count, producing the reported uninterruptible hung task in __anon_vma_prepare(); repeated poisoned roots can block further faults and rmap operations."
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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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"mm/rmap.c",
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"mm/vma.c"
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"lessThanOrEqual": "6.18.*",
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"status": "unaffected",
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},
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{
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"version": "7.2.9",
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"lessThanOrEqual": "7.2.*",
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"status": "unaffected",
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},
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{
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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"references": [
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},
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{
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"url": "https://git.kernel.org/stable/c/aef0f69b515af1c8a4147f68a46b6b81854f46f7"
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},
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{
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},
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"url": "https://git.kernel.org/stable/c/465e222815c8839445d09028fa4c77e70f7f1c7d"
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},
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{
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"url": "https://git.kernel.org/stable/c/a500df43cde075f6ea4b8bae495d89f2c35b3e16"
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},
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{
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"url": "https://git.kernel.org/stable/c/4cef512a955e4008ae4436a4fc97726976df1fdf"
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},
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{
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"url": "https://git.kernel.org/stable/c/d348a715380bfcc6a611bdf722169d53fd01e735"
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},
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{
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"url": "https://git.kernel.org/stable/c/b6ac0b3f6013c168f22cad97e79967accacb08e1"
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}
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],
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"title": "mm/rmap: fix missing barrier between anon_vma init and vma->anon_vma publish",
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