CVE-2026-53393nfsd: reset write verifier on deferred writeback errors

Official description

In the Linux kernel, the following vulnerability has been resolved: nfsd: reset write verifier on deferred writeback errors nfsd_vfs_write() and nfsd_commit() both call filemap_check_wb_err() to detect deferred writeback errors, but neither rotates the server's write verifier (nn->writeverf) when this check fails. Every other durable-storage-failure path in these functions calls commit_reset_write_verifier() before returning an error. The missing rotation means clients holding UNSTABLE write data under the current verifier will COMMIT, receive the unchanged verifier back, and conclude their data is durable — silently dropping data that failed writeback. This violates the UNSTABLE+COMMIT durability contract (RFC 1813 §3.3.7, RFC 8881 §18.32). Add commit_reset_write_verifier() calls at both filemap_check_wb_err() error sites, matching the pattern used by adjacent error paths in the same functions. The helper already filters -EAGAIN and -ESTALE internally, so the calls are unconditionally safe.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/b8e5894e56cff70fa245628fe16f0ad6367f8090
• https://git.kernel.org/stable/c/bc2baca02ec56da7707a74ed5d340b0a1dff1841
• https://git.kernel.org/stable/c/43b65d2997963e80e8d8d86520bcb1e0751227de
• https://git.kernel.org/stable/c/666e837b247fcadf2d8d508b9b0e49d720393eb4
• https://git.kernel.org/stable/c/1dd664b39774a9c89b72de8e59bf9ef4b3aaff2e
• https://git.kernel.org/stable/c/4367afc119c51e17a616f6908772b7e2c2c4013f
• https://git.kernel.org/stable/c/b027cca33c97354149fcc0ddeede4525c41093cd
• https://git.kernel.org/stable/c/2090b05803faab8a9fa62fbff871007862cac1b7