GHSA-JR3F-X4P8-9X32
Vulnerability from github – Published: 2026-10-18 18:31 – Updated: 2026-10-30 15:33In the Linux kernel, the following vulnerability has been resolved:
mm/rmap: fix missing barrier between anon_vma init and vma->anon_vma publish
On arm64 server, we find that a task trying to grab the anon_vma lock triggers hungtask.
INFO: task main:2354726 blocked for more than 120 seconds. Tainted: G E 5.10.0-0021.aarch64 #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:main state:D stack: 0 pid:2354726 ppid:2350673 flags:0x00000a01 Call trace: __switch_to+0x7c/0xbc __schedule+0x3b4/0x8a0 schedule+0x50/0xe0 rwsem_down_write_slowpath+0x3cc/0x6cc down_write+0x60/0x260 __anon_vma_prepare+0x6c/0x210 do_anonymous_page+0x258/0x660 handle_pte_fault+0x188/0x214 __handle_mm_fault+0x1b0/0x380 handle_mm_fault+0xf4/0x284 do_page_fault+0x19c/0x494 do_translation_fault+0xcc/0xf8 do_mem_abort+0x48/0xac el0_da+0x44/0x80 el0_sync_handler+0x88/0xb4 el0_sync+0x160/0x180
After analyzing the vmcore, we found the anon_vma->root->rwsem.count is -1. There is another anon_vma whose anon_vma->root->rwsem.count is 1, the anon_vma->root->rwsem.owner shows the lock is held, but the stack of the task shows the task doesn't hold the anon_vma lock.
After adding more debugging info, we found __anon_vma_prepare() reuses anon_vma and triggers the UAF of anon_vma->root due to missing memory barrier, leading to locking and unlocking two different anon_vma->root, thus leading to an anon_vma will never be unlocked, and another anon_vma couldn't be locked anymore.
This race requires two adjacent VMAs that are not merged but are anon_vma-compatible (e.g., they differ in VMA_ACCESS_FLAGS that can be changed by mprotect()). Two threads fault on each VMA concurrently, both calling __anon_vma_prepare() with only mmap_lock held for reading.
THREAD A THREAD B
__anon_vma_prepare __anon_vma_prepare find_mergeable_anon_vma() -> NULL anon_vma = anon_vma_alloc(); anon_vma->root = anon_vma; // the two stores may be reordered vma->anon_vma = anon_vma; // finds A's anon_vma anon_vma = find_mergeable_anon_vma(vma); anon_vma_lock_write(anon_vma); // may still see the old root down_write(&anon_vma->root->rwsem); anon_vma_unlock_write(anon_vma); // see the new root, never unlock old up_write(&anon_vma->root->rwsem);
thread A triggers page fault and calls __anon_vma_prepare() to prepare anon_vma for the faulting vma. __anon_vma_prepare() allocates and initializes a new anon_vma, and then publishes it to the vma with a plain store. anon_vma_prepare() only requires the mmap_lock to be held for reading, so two threads can fault on adjacent VMAs at the same time. While thread A publishes a new anon_vma, thread B could find the anon_vma via find_mergeable_anon_vma() and then locks anon_vma->root->rwsem.
The store to anon_vma->root in anon_vma_alloc() and the store to vma->anon_vma can be reordered. The anon_vma_lock_write() and spin_lock() only provide acquire semantics, which do not prevent prior stores from being reordered after them. The release semantics of the corresponding spin_unlock() and anon_vma_unlock_write() come too late, the store to vma->anon_vma is already published before they take effect. As a result, thread B can observe the following order:
vma->anon_vma = anon_vma;
anon_vma->root = anon_vma;
The anon_vma slab is SLAB_TYPESAFE_BY_RCU, so a newly allocated anon_vma may reuse memory from a previously freed one. The constructor (anon_vma_ctor) does not reset anon_vma->root, and __put_anon_vma() doesn't clear it either, so the old root value persists until anon_vma_alloc() overwrites it. If that store isn't v ---truncated---
{
"affected": [],
"aliases": [
"CVE-2026-98507"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-18T16:17:01Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/rmap: fix missing barrier between anon_vma init and vma-\u003eanon_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 \u003e /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-\u003eroot-\u003erwsem.count is\n-1. There is another anon_vma whose anon_vma-\u003eroot-\u003erwsem.count is 1, the\nanon_vma-\u003eroot-\u003erwsem.owner shows the lock is held, but the stack of the\ntask shows the task doesn\u0027t 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-\u003eroot due to missing memory\nbarrier, leading to locking and unlocking two different anon_vma-\u003eroot,\nthus leading to an anon_vma will never be unlocked, and another anon_vma\ncouldn\u0027t 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() -\u003e NULL\n anon_vma = anon_vma_alloc();\n anon_vma-\u003eroot = anon_vma;\n // the two stores may be reordered\n vma-\u003eanon_vma = anon_vma;\n // finds A\u0027s 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(\u0026anon_vma-\u003eroot-\u003erwsem);\n anon_vma_unlock_write(anon_vma);\n // see the new root, never unlock old\n up_write(\u0026anon_vma-\u003eroot-\u003erwsem);\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-\u003eroot-\u003erwsem.\n\nThe store to anon_vma-\u003eroot in anon_vma_alloc() and the store to\nvma-\u003eanon_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-\u003eanon_vma is already published before they take effect. As a result,\nthread B can observe the following order:\n\n vma-\u003eanon_vma = anon_vma;\n anon_vma-\u003eroot = 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-\u003eroot, and __put_anon_vma()\ndoesn\u0027t clear it either, so the old root value persists until\nanon_vma_alloc() overwrites it. If that store isn\u0027t v\n---truncated---",
"id": "GHSA-jr3f-x4p8-9x32",
"modified": "2026-10-30T15:33:53Z",
"published": "2026-10-18T18:31:51Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98507"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/465e222815c8839445d09028fa4c77e70f7f1c7d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4cef512a955e4008ae4436a4fc97726976df1fdf"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7d103fc7b836084af585d9d3471334624354cf26"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a500df43cde075f6ea4b8bae495d89f2c35b3e16"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/aef0f69b515af1c8a4147f68a46b6b81854f46f7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b6ac0b3f6013c168f22cad97e79967accacb08e1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/badedec499f6320742368c73fa77cd63dcf8ca55"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d348a715380bfcc6a611bdf722169d53fd01e735"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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