nfsd: reset write verifier on deferred writeback errors

Summary

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.

Timeline

1. Jul 19, 2026, 12:01 PM UTCCVE published
2. Aug 17, 2026, 4:50 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 5.10.124 · fixed in 5.10.261; From 5.15.49 · fixed in 5.15.212

• Linux Linux

  5.17

References 8