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NFSD: Fix "start of NFS reply" pointer passed to nfsd_cache_update()

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[ Upstream commit 1caf5f61dd ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Chuck Lever 2023-11-28 16:58:34 -05:00 committed by Greg Kroah-Hartman
parent bd3a9e5771
commit ed1e0ea241
1 changed files with 3 additions and 1 deletions
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4
fs/nfsd/nfssvc.c
View file

@ -988,6 +988,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
const struct svc_procedure *proc = rqstp->rq_procinfo;
__be32 *statp = rqstp->rq_accept_statp;
struct nfsd_cacherep *rp;
__be32 *nfs_reply;
/*
* Give the xdr decoder a chance to change this if it wants
@ -1008,6 +1009,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
goto out_dropit;
}
nfs_reply = xdr_inline_decode(&rqstp->rq_res_stream, 0);
*statp = proc->pc_func(rqstp);
if (test_bit(RQ_DROPME, &rqstp->rq_flags))
goto out_update_drop;
@ -1015,7 +1017,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
if (!proc->pc_encode(rqstp, &rqstp->rq_res_stream))
goto out_encode_err;
nfsd_cache_update(rqstp, rp, rqstp->rq_cachetype, statp + 1);
nfsd_cache_update(rqstp, rp, rqstp->rq_cachetype, nfs_reply);
out_cached_reply:
return 1;