NFSD: Prevent client use-after-free during admin state revocation

Summary

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during admin state revocation A stateid holds only a bare pointer to its nfs4_client; a stateid reference does not pin it. The client survives only because __destroy_client() drains its stateids before free_client() runs. nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(), which dereferences the client to revoke a stateid and read clp->cl_minorversion. A teardown racing the dropped lock can free the client first. Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero. force_expire_client() ignores it: once its wait for cl_rpc_users to reach zero has passed, a later pin goes unnoticed. Under client_lock, skip a client whose cl_time is already zero -- force_expire_client() clears it there before waiting -- otherwise pin cl_rpc_users before dropping the lock. The walk then either sees the expiry and skips, or pins in time for that wait to cover the revoke.

Timeline

1. Sep 11, 2026, 7:45 PM UTCCVE published
2. Oct 19, 2026, 8:50 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc · fixed in e1ba4d3c5bfdca3f013b8cbc829ae2f7975d8608; From 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc · fixed in 549bd9868e9d77b07ea94870940d64342829c6ad; From 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc · fixed in bf1f948691523282cc4905bc6cd325e0c0b49e6a; From 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc · fixed in e270e5a0778e5bff852c8862ce9576ce70359393

• Linux Linux

  6.9

• KernelLinux

  From 6.9.0 · fixed in 6.12.111; From 6.13.0 · fixed in 6.18.51; From 6.19.0 · fixed in 7.2.4

References 4