nfsd: don't free session slots that are still in use
Summary
| CVE | CVE-2026-89689 |
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| State | PUBLISHED |
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| Assigner | Linux |
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| Source Priority | CVE Program / NVD first with legacy fallback |
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| Published | 2026-09-11 20:19:55 UTC |
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| Updated | 2026-09-11 20:19:55 UTC |
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| Description | In the Linux kernel, the following vulnerability has been resolved:
nfsd: don't free session slots that are still in use
nfsd4_sequence() can free the very slot it is currently processing.
When the session shrinker has reduced se_target_maxslots below
se_fchannel.maxreqs, the shrink path checks three conditions before
calling free_session_slots():
1. se_target_maxslots < maxreqs (shrink was advertised)
2. slot->sl_generation == se_slot_gen (slot is up-to-date)
3. seq->maxslots <= se_target_maxslots (client acknowledges)
However, seq->slotid is never checked against se_target_maxslots.
A client using a slot in the range [se_target_maxslots, maxreqs) can
satisfy all three conditions: its slot has the current generation
(set by a prior SEQUENCE), and it sends sa_highest_slotid <=
se_target_maxslots to acknowledge the reduction.
free_session_slots() then kfrees every slot at index >=
se_target_maxslots, including the caller's own slot. The function
continues to write sl_seqid, sl_flags, sl_generation, and stores the
dangling pointer in cstate->slot. Later, nfsd4_store_cache_entry()
copies up to maxresp_cached bytes of the compound reply into the freed
sl_data[] array, corrupting whatever slab object now occupies that
address.
Additionally, a concurrent thread processing SEQUENCE on a different
high-numbered slot can have its slot freed out from under it.
NFSD4_SLOT_INUSE is set under nn->client_lock before the lock is
released, so any concurrent thread past SEQUENCE will have its slot
marked. However, free_session_slots() does not check NFSD4_SLOT_INUSE
before freeing.
Fix both problems by:
1. Checking that the current request's slotid is below the shrink
boundary.
2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and
deferring the shrink if any are active. |
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Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
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| CNA |
Linux |
Linux |
affected fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 72d40b103bb03f0124d3a3c8f71a30cbafaf6afa git |
Not specified |
| CNA |
Linux |
Linux |
affected fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 b449b134e7762ddf98653a4b1d3e76d2d212ea64 git |
Not specified |
| CNA |
Linux |
Linux |
affected fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 f5d22e372f4ac3eb287037a488c29691d52a6330 git |
Not specified |
| CNA |
Linux |
Linux |
affected 6.14 |
Not specified |
| CNA |
Linux |
Linux |
unaffected 6.14 semver |
Not specified |
| CNA |
Linux |
Linux |
unaffected 6.18.50 6.18.* semver |
Not specified |
| CNA |
Linux |
Linux |
unaffected 7.2.4 7.2.* semver |
Not specified |
| CNA |
Linux |
Linux |
unaffected 7.3-rc1 * original_commit_for_fix |
Not specified |
References
| Reference | Source | Link | Tags |
|---|
| git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa |
416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
git.kernel.org |
|
| git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330 |
416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
git.kernel.org |
|
| git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64 |
416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
git.kernel.org |
|
| CVE Program record |
CVE.ORG |
www.cve.org |
canonical |
| NVD vulnerability detail |
NVD |
nvd.nist.gov |
canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.