UBUNTU-CVE-2026-89679: High severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix null dereference in nfsd4setattr for deleg timestamp attrs When a SETATTR request includes FATTR4WORD2TIMEDELEGACCESS or FATTR4WORD2TIMEDELEGMODIFY in the attribute bitmap, nfsd4setattr() sets delegattrs=true and calls nfs4preprocessstateidop() to validate the stateid. If the client supplies the NFSv4 "one stateid" (all-0xFF bytes), checkspecialstateids() returns nfsok without populating the output nfs4stid pointer, because the special-stateid path in nfs4preprocessstateidop() jumps to done: with s==NULL, and the "if (s)" block that would set cstid is skipped. The local variable st remains NULL. Back in nfsd4setattr(), the if (delegattrs) block then unconditionally dereferences st->sctype (at offset 4 from NULL), causing a kernel oops. This is remotely triggerable by any NFSv4 client: send COMPOUND [PUTROOTFH, SETATTR(ONESTATEID, {bmval2=FATTR4WORD2TIMEDELEGACCESS, ...})]. No authentication, delegation, or prior state is required. Fix by adding a NULL check before the dereference. A special stateid is not a delegation stateid, so the existing nfserrbadstateid return value is already correct; we only need to guard the pointer dereference itself.