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The "statp + 1" pointer that is passed to nfsd_cache_update() is supposed to point to the start of the egress NFS Reply header. In fact, it does point there for AUTH_SYS and RPCSEC_GSS_KRB5 requests. But both krb5i and krb5p add fields between the RPC header's accept_stat field and the start of the NFS Reply header. In those cases, "statp + 1" points at the extra fields instead of the Reply. The result is that nfsd_cache_update() caches what looks to the client like garbage. A connection break can occur for a number of reasons, but the most common reason when using krb5i/p is a GSS sequence number window underrun. When an underrun is detected, the server is obliged to drop the RPC and the connection to force a retransmit with a fresh GSS sequence number. The client presents the same XID, it hits in the server's DRC, and the server returns the garbage cache entry. The "statp + 1" argument has been used since the oldest changeset in the kernel history repo, so it has been in nfsd_dispatch() literally since before history began. The problem arose only when the server-side GSS implementation was added twenty years ago. Reviewed-by: Jeff Layton <jlayton@kernel.org> Tested-by: Jeff Layton <jlayton@kernel.org Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.