From 1caf5f61dd8430ae5a0b4538afe4953ce7517cbb Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Fri, 10 Nov 2023 11:28:33 -0500 Subject: NFSD: Fix "start of NFS reply" pointer passed to nfsd_cache_update() 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 Tested-by: Jeff Layton --- fs/nfsd/nfssvc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index d6122bb2d167..b4e4e04f9931 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -981,6 +981,7 @@ 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 @@ -1010,6 +1011,7 @@ 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; @@ -1023,7 +1025,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp) */ smp_store_release(&rqstp->rq_status_counter, rqstp->rq_status_counter + 1); - 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; -- cgit v1.2.3