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.
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.
Published:
2026-09-11
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
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 |
|
||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No remediation available yet.
Tracking
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Advisories
No advisories yet.
References
History
Fri, 11 Sep 2026 23:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | nfsd: don't free session slots that are still in use | |
| 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: 2026-09-11T19:46:09.976Z
Reserved: 2026-09-11T19:38:34.749Z
Link: CVE-2026-89689
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-11T20:19:55.900
Modified: 2026-09-11T20:19:55.900
Link: CVE-2026-89689
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.