nfsd: defer vfree of compound ops to fix rpc_status UAF

Overview

In the Linux kernel, the following vulnerability has been resolved:

nfsd: defer vfree of compound ops to fix rpc_status UAF

The rpc_status netlink dumpit walks every in-flight svc_rqst under rcu_read_lock and, for NFSv4 requests, reads opnums out of args->ops[]. But args->ops is a separate vmalloc buffer freed synchronously by vfree() in nfsd4_release_compoundargs() at the end of every compound. The dumpit's rcu_read_lock pins the svc_rqst struct itself (freed via kfree_rcu), but nothing defers the vfree of the ops buffer across the RCU grace period. A concurrent compound completion can therefore free the buffer while the dumpit is reading it — a use-after-free on vmalloc memory.

The trailing seqcount recheck (smp_load_acquire of rq_status_counter) cannot undo a load that already retired against freed memory.

Fix by replacing vfree(args->ops) with kvfree_rcu_mightsleep(), which defers the free until after an RCU grace period. This makes the existing rcu_read_lock in the dumpit sufficient to protect the read. The tradeoff is that completed compound ops buffers (up to 200 * sizeof(struct nfsd4_op)) persist in memory slightly longer, across one grace period, before being reclaimed.

Affected

• Linux >= bd9d6a3efa9709e653aafbeb859289feccb8e70c < 48f72aff24f7a7329209dc6cbc27c869f3e3595c
• Linux >= bd9d6a3efa9709e653aafbeb859289feccb8e70c < 6703199f4d7e7f37d6a726a849eb358e8fae72fb
• Linux >= bd9d6a3efa9709e653aafbeb859289feccb8e70c < 19413ccc45070a7270b9e25c2a258daf7f91de42
• Linux >= bd9d6a3efa9709e653aafbeb859289feccb8e70c < fca26a3fc19ed02278aa2a150af82d43db0302cb
• Linux 6.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4, Red Hat Enterprise Linux 6 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-21 · vex