CVE-2026-22980
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.
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 3.18 | 5.10.248 |
| linux / linux_kernel | 5.11 | 5.15.198 |
| linux / linux_kernel | 5.16 | 6.1.161 |
| linux / linux_kernel | 6.2 | 6.6.121 |
| linux / linux_kernel | 6.7 | 6.12.66 |
| linux / linux_kernel | 6.13 | 6.18.6 |
| linux / linux_kernel | 6.19-rc1 | 6.19-rc1.x |
| linux / linux_kernel | 6.19-rc2 | 6.19-rc2.x |
| linux / linux_kernel | 6.19-rc3 | 6.19-rc3.x |
| linux / linux_kernel | 6.19-rc4 | 6.19-rc4.x |
- https://git.kernel.org/stable/c/06600719d0f7a723811c45e4d51f5b742f345309
- https://git.kernel.org/stable/c/2857bd59feb63fcf40fe4baf55401baea6b4feb4
- https://git.kernel.org/stable/c/34eb22836e0cdba093baac66599d68c4cd245a9d
- https://git.kernel.org/stable/c/53f07d095e7e680c5e4569a55a019f2c0348cdc6
- https://git.kernel.org/stable/c/ba4811c8b433bfa681729ca42cc62b6034f223b0
- https://git.kernel.org/stable/c/ca97360860eb02e3ae4ba42c19b439a0fcecbf06
- https://git.kernel.org/stable/c/e8bfa2401d4c51eca6e48e9b33c798828ca9df61
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