Description
In 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---
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---
Published:
2026-10-18
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
|
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Remediation
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
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References
History
Sun, 18 Oct 2026 15:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In 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--- | |
| Title | mm/rmap: fix missing barrier between anon_vma init and vma->anon_vma publish | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-18T15:17:13.767Z
Reserved: 2026-09-25T10:25:14.354Z
Link: CVE-2026-98507
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.