In the Linux kernel, the following vulnerability has been resolved:
RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency
Commit 51976c6cd786 ("RDMA/core: Provide rdma_user_mmap_disassociate()
to disassociate mmap pages") introduced disassociation_lock to protect
new mmap registrations against uverbs_user_mmap_disassociate(), but
created an ABBA deadlock:
Thread A (mmap / fork):
mmap_lock -> disassociation_lock
Thread B (disassociate):
disassociation_lock -> mmap_lock
Fix by removing disassociation_lock entirely and using the pre-existing
hw_destroy_rwsem instead. hw_destroy_rwsem already provides the same
protection: rdma_umap_open() and ib_uverbs_mmap() both use
down_read_trylock() before registering a new VMA, so holding hw_destroy_rwsem
in uverbs_user_mmap_disassociate() is sufficient to block new registrations.
trylock is used in both mmap paths (not blocking down_read) because
mmap_lock is already held on entry, and uverbs_user_mmap_disassociate()
acquires mmap_lock internally — a blocking read would recreate the same
deadlock.
The only caller that was not taking hw_destroy_rwsem for write was
rdma_user_mmap_disassociate(). Fix it to take the rwsem per-ufile while
iterating under lists_mutex. This is safe because ib_uverbs_close()
releases hw_destroy_rwsem entirely before acquiring lists_mutex, so the
two locks are never held simultaneously.
lockdep warning:
[ 776.654252] ======================================================
[ 776.655214] WARNING: possible circular locking dependency detected
[ 776.656167] 6.18.0for-upstream_debug_94e244d9ccab #1 Not tainted
[ 776.657114] ------------------------------------------------------
[ 776.658087] devlink/14824 is trying to acquire lock:
[ 776.658879] ffff88811170c800 (&mm->mmap_lock){++++}-{4:4}, at: uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs]
[ 776.660479]
[ 776.660479] but task is already holding lock:
[ 776.661460] ffff888142d92b08 (&file->disassociation_lock){+.+.}-{4:4}, at: uverbs_user_mmap_disassociate+0x39/0x780 [ib_uverbs]
[ 776.663177]
[ 776.663177] which lock already depends on the new lock.
[ 776.663177]
[ 776.664525]
[ 776.664525] the existing dependency chain (in reverse order) is:
[ 776.665724]
[ 776.665724] -> #2 (&file->disassociation_lock){+.+.}-{4:4}:
[ 776.666887] __mutex_lock+0x16d/0x2330
[ 776.667633] rdma_umap_open+0x129/0x280 [ib_uverbs]
[ 776.668489] dup_mmap+0xa40/0x1790
[ 776.669170] copy_process+0x5dd2/0x6170
[ 776.669933] kernel_clone+0xb6/0x610
[ 776.670636] __do_sys_clone+0xb5/0xf0
[ 776.671354] do_syscall_64+0x70/0x12e0
[ 776.672083] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 776.672940]
[ 776.672940] -> #1 (&mm->mmap_lock/1){+.+.}-{4:4}:
[ 776.673985] down_write_nested+0x90/0x1e0
[ 776.674751] dup_mmap+0x201/0x1790
[ 776.675448] copy_process+0x5dd2/0x6170
[ 776.676180] kernel_clone+0xb6/0x610
[ 776.676904] __do_sys_clone+0xb5/0xf0
[ 776.677615] do_syscall_64+0x70/0x12e0
[ 776.678351] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 776.679239]
[ 776.679239] -> #0 (&mm->mmap_lock){++++}-{4:4}:
[ 776.680253] __lock_acquire+0x18c6/0x2ec0
[ 776.681018] lock_acquire+0x10e/0x2e0
[ 776.681742] down_read+0x95/0x430
[ 776.682395] uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs]
[ 776.683436] uverbs_destroy_ufile_hw+0x1ae/0x270 [ib_uverbs]
[ 776.684416] ib_uverbs_remove_one+0x22b/0x420 [ib_uverbs]
[ 776.685371] remove_client_context+0xa6/0xf0 [ib_core]
[ 776.686342] disable_device+0x12b/0x240 [ib_core]
[ 776.687249] __ib_unregister_device+0x269/0x460 [ib_core]
[ 776.688233] ib_unregister_device+0x21/0x30 [ib_core]
[ 776.689140] mlx5r_remove+0xd0/0x170 [mlx5_ib]
[ 776.689999] device_release_driver_internal+0x3b2/0x5
---truncated---
RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency
Commit 51976c6cd786 ("RDMA/core: Provide rdma_user_mmap_disassociate()
to disassociate mmap pages") introduced disassociation_lock to protect
new mmap registrations against uverbs_user_mmap_disassociate(), but
created an ABBA deadlock:
Thread A (mmap / fork):
mmap_lock -> disassociation_lock
Thread B (disassociate):
disassociation_lock -> mmap_lock
Fix by removing disassociation_lock entirely and using the pre-existing
hw_destroy_rwsem instead. hw_destroy_rwsem already provides the same
protection: rdma_umap_open() and ib_uverbs_mmap() both use
down_read_trylock() before registering a new VMA, so holding hw_destroy_rwsem
in uverbs_user_mmap_disassociate() is sufficient to block new registrations.
trylock is used in both mmap paths (not blocking down_read) because
mmap_lock is already held on entry, and uverbs_user_mmap_disassociate()
acquires mmap_lock internally — a blocking read would recreate the same
deadlock.
The only caller that was not taking hw_destroy_rwsem for write was
rdma_user_mmap_disassociate(). Fix it to take the rwsem per-ufile while
iterating under lists_mutex. This is safe because ib_uverbs_close()
releases hw_destroy_rwsem entirely before acquiring lists_mutex, so the
two locks are never held simultaneously.
lockdep warning:
[ 776.654252] ======================================================
[ 776.655214] WARNING: possible circular locking dependency detected
[ 776.656167] 6.18.0for-upstream_debug_94e244d9ccab #1 Not tainted
[ 776.657114] ------------------------------------------------------
[ 776.658087] devlink/14824 is trying to acquire lock:
[ 776.658879] ffff88811170c800 (&mm->mmap_lock){++++}-{4:4}, at: uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs]
[ 776.660479]
[ 776.660479] but task is already holding lock:
[ 776.661460] ffff888142d92b08 (&file->disassociation_lock){+.+.}-{4:4}, at: uverbs_user_mmap_disassociate+0x39/0x780 [ib_uverbs]
[ 776.663177]
[ 776.663177] which lock already depends on the new lock.
[ 776.663177]
[ 776.664525]
[ 776.664525] the existing dependency chain (in reverse order) is:
[ 776.665724]
[ 776.665724] -> #2 (&file->disassociation_lock){+.+.}-{4:4}:
[ 776.666887] __mutex_lock+0x16d/0x2330
[ 776.667633] rdma_umap_open+0x129/0x280 [ib_uverbs]
[ 776.668489] dup_mmap+0xa40/0x1790
[ 776.669170] copy_process+0x5dd2/0x6170
[ 776.669933] kernel_clone+0xb6/0x610
[ 776.670636] __do_sys_clone+0xb5/0xf0
[ 776.671354] do_syscall_64+0x70/0x12e0
[ 776.672083] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 776.672940]
[ 776.672940] -> #1 (&mm->mmap_lock/1){+.+.}-{4:4}:
[ 776.673985] down_write_nested+0x90/0x1e0
[ 776.674751] dup_mmap+0x201/0x1790
[ 776.675448] copy_process+0x5dd2/0x6170
[ 776.676180] kernel_clone+0xb6/0x610
[ 776.676904] __do_sys_clone+0xb5/0xf0
[ 776.677615] do_syscall_64+0x70/0x12e0
[ 776.678351] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 776.679239]
[ 776.679239] -> #0 (&mm->mmap_lock){++++}-{4:4}:
[ 776.680253] __lock_acquire+0x18c6/0x2ec0
[ 776.681018] lock_acquire+0x10e/0x2e0
[ 776.681742] down_read+0x95/0x430
[ 776.682395] uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs]
[ 776.683436] uverbs_destroy_ufile_hw+0x1ae/0x270 [ib_uverbs]
[ 776.684416] ib_uverbs_remove_one+0x22b/0x420 [ib_uverbs]
[ 776.685371] remove_client_context+0xa6/0xf0 [ib_core]
[ 776.686342] disable_device+0x12b/0x240 [ib_core]
[ 776.687249] __ib_unregister_device+0x269/0x460 [ib_core]
[ 776.688233] ib_unregister_device+0x21/0x30 [ib_core]
[ 776.689140] mlx5r_remove+0xd0/0x170 [mlx5_ib]
[ 776.689999] device_release_driver_internal+0x3b2/0x5
---truncated---
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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Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
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References
History
Wed, 14 Oct 2026 13:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency Commit 51976c6cd786 ("RDMA/core: Provide rdma_user_mmap_disassociate() to disassociate mmap pages") introduced disassociation_lock to protect new mmap registrations against uverbs_user_mmap_disassociate(), but created an ABBA deadlock: Thread A (mmap / fork): mmap_lock -> disassociation_lock Thread B (disassociate): disassociation_lock -> mmap_lock Fix by removing disassociation_lock entirely and using the pre-existing hw_destroy_rwsem instead. hw_destroy_rwsem already provides the same protection: rdma_umap_open() and ib_uverbs_mmap() both use down_read_trylock() before registering a new VMA, so holding hw_destroy_rwsem in uverbs_user_mmap_disassociate() is sufficient to block new registrations. trylock is used in both mmap paths (not blocking down_read) because mmap_lock is already held on entry, and uverbs_user_mmap_disassociate() acquires mmap_lock internally — a blocking read would recreate the same deadlock. The only caller that was not taking hw_destroy_rwsem for write was rdma_user_mmap_disassociate(). Fix it to take the rwsem per-ufile while iterating under lists_mutex. This is safe because ib_uverbs_close() releases hw_destroy_rwsem entirely before acquiring lists_mutex, so the two locks are never held simultaneously. lockdep warning: [ 776.654252] ====================================================== [ 776.655214] WARNING: possible circular locking dependency detected [ 776.656167] 6.18.0for-upstream_debug_94e244d9ccab #1 Not tainted [ 776.657114] ------------------------------------------------------ [ 776.658087] devlink/14824 is trying to acquire lock: [ 776.658879] ffff88811170c800 (&mm->mmap_lock){++++}-{4:4}, at: uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs] [ 776.660479] [ 776.660479] but task is already holding lock: [ 776.661460] ffff888142d92b08 (&file->disassociation_lock){+.+.}-{4:4}, at: uverbs_user_mmap_disassociate+0x39/0x780 [ib_uverbs] [ 776.663177] [ 776.663177] which lock already depends on the new lock. [ 776.663177] [ 776.664525] [ 776.664525] the existing dependency chain (in reverse order) is: [ 776.665724] [ 776.665724] -> #2 (&file->disassociation_lock){+.+.}-{4:4}: [ 776.666887] __mutex_lock+0x16d/0x2330 [ 776.667633] rdma_umap_open+0x129/0x280 [ib_uverbs] [ 776.668489] dup_mmap+0xa40/0x1790 [ 776.669170] copy_process+0x5dd2/0x6170 [ 776.669933] kernel_clone+0xb6/0x610 [ 776.670636] __do_sys_clone+0xb5/0xf0 [ 776.671354] do_syscall_64+0x70/0x12e0 [ 776.672083] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [ 776.672940] [ 776.672940] -> #1 (&mm->mmap_lock/1){+.+.}-{4:4}: [ 776.673985] down_write_nested+0x90/0x1e0 [ 776.674751] dup_mmap+0x201/0x1790 [ 776.675448] copy_process+0x5dd2/0x6170 [ 776.676180] kernel_clone+0xb6/0x610 [ 776.676904] __do_sys_clone+0xb5/0xf0 [ 776.677615] do_syscall_64+0x70/0x12e0 [ 776.678351] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [ 776.679239] [ 776.679239] -> #0 (&mm->mmap_lock){++++}-{4:4}: [ 776.680253] __lock_acquire+0x18c6/0x2ec0 [ 776.681018] lock_acquire+0x10e/0x2e0 [ 776.681742] down_read+0x95/0x430 [ 776.682395] uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs] [ 776.683436] uverbs_destroy_ufile_hw+0x1ae/0x270 [ib_uverbs] [ 776.684416] ib_uverbs_remove_one+0x22b/0x420 [ib_uverbs] [ 776.685371] remove_client_context+0xa6/0xf0 [ib_core] [ 776.686342] disable_device+0x12b/0x240 [ib_core] [ 776.687249] __ib_unregister_device+0x269/0x460 [ib_core] [ 776.688233] ib_unregister_device+0x21/0x30 [ib_core] [ 776.689140] mlx5r_remove+0xd0/0x170 [mlx5_ib] [ 776.689999] device_release_driver_internal+0x3b2/0x5 ---truncated--- | |
| Title | RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-14T13:27:56.162Z
Reserved: 2026-09-25T10:25:14.348Z
Link: CVE-2026-98431
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-14T14:17:54.887
Modified: 2026-10-14T14:17:54.887
Link: CVE-2026-98431
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.