Bug 2419946 (CVE-2025-40326)

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Define actions for the new time_deleg FATTR4 attributes

NFSv4 clients won't send legitimate GETATTR requests for these new
attributes because they are intended to be used only with CB_GETATTR
and SETATTR. But NFSD has to do something besides crashing if it
ever sees a GETATTR request that queries these attributes.

RFC 8881 Section 18.7.3 states:

> The server MUST return a value for each attribute that the client
> requests if the attribute is supported by the server for the
> target file system. If the server does not support a particular
> attribute on the target file system, then it MUST NOT return the
> attribute value and MUST NOT set the attribute bit in the result
> bitmap. The server MUST return an error if it supports an
> attribute on the target but cannot obtain its value. In that case,
> no attribute values will be returned.

Further, RFC 9754 Section 5 states:

> These new attributes are invalid to be used with GETATTR, VERIFY,
> and NVERIFY, and they can only be used with CB_GETATTR and SETATTR
> by a client holding an appropriate delegation.

Thus there does not appear to be a specific server response mandated
by specification. Taking the guidance that querying these attributes
via GETATTR is "invalid", NFSD will return nfserr_inval, failing the
request entirely.