# CVE-2026-98431: RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency

CVE-2026-98431 is fixed in linux on 1 platform by DEBIAN-CVE-2026-98431 (version 7.2.8-1), released October 16, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98431
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 14, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98431

## 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---

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.8-1 | [DEBIAN-CVE-2026-98431](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98431.md) | Oct 16, 2026 |

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