CVE-2026-22980nfsd: provide locking for v4_end_grace

Official description

In the Linux kernel, the following vulnerability has been resolved: nfsd: provide locking for v4_end_grace Writing to v4_end_grace can race with server shutdown and result in memory being accessed after it was freed - reclaim_str_hashtbl in particularly. We cannot hold nfsd_mutex across the nfsd4_end_grace() call as that is held while client_tracking_op->init() is called and that can wait for an upcall to nfsdcltrack which can write to v4_end_grace, resulting in a deadlock. nfsd4_end_grace() is also called by the landromat work queue and this doesn't require locking as server shutdown will stop the work and wait for it before freeing anything that nfsd4_end_grace() might access. However, we must be sure that writing to v4_end_grace doesn't restart the work item after shutdown has already waited for it. For this we add a new flag protected with nn->client_lock. It is set only while it is safe to make client tracking calls, and v4_end_grace only schedules work while the flag is set with the spinlock held. So this patch adds a nfsd_net field "client_tracking_active" which is set as described. Another field "grace_end_forced", is set when v4_end_grace is written. After this is set, and providing client_tracking_active is set, the laundromat is scheduled. This "grace_end_forced" field bypasses other checks for whether the grace period has finished. This resolves a race which can result in use-after-free.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ca97360860eb02e3ae4ba42c19b439a0fcecbf06
• https://git.kernel.org/stable/c/e8bfa2401d4c51eca6e48e9b33c798828ca9df61
• https://git.kernel.org/stable/c/34eb22836e0cdba093baac66599d68c4cd245a9d
• https://git.kernel.org/stable/c/06600719d0f7a723811c45e4d51f5b742f345309
• https://git.kernel.org/stable/c/ba4811c8b433bfa681729ca42cc62b6034f223b0
• https://git.kernel.org/stable/c/53f07d095e7e680c5e4569a55a019f2c0348cdc6
• https://git.kernel.org/stable/c/2857bd59feb63fcf40fe4baf55401baea6b4feb4
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html