[PATCH 5.15 068/164] nfsd: never defer requests during idmap lookup

Sasha Levin
2026-02-28T18:16:02Z

From: Anthony Iliopoulos <ailiop@suse.com>

[ Upstream commit f9c206cdc4266caad6a9a7f46341420a10f03ccb ]

During v4 request compound arg decoding, some ops (e.g. SETATTR)
can trigger idmap lookup upcalls. When those upcall responses get
delayed beyond the allowed time limit, cache_check() will mark the
request for deferral and cause it to be dropped.

This prevents nfs4svc_encode_compoundres from being executed, and
thus the session slot flag NFSD4_SLOT_INUSE never gets cleared.
Subsequent client requests will fail with NFSERR_JUKEBOX, given
that the slot will be marked as in-use, making the SEQUENCE op
fail.

Fix this by making sure that the RQ_USEDEFERRAL flag is always
clear during nfs4svc_decode_compoundargs(), since no v4 request
should ever be deferred.

Fixes: 2f425878b6a7 ("nfsd: don't use the deferral service, return NFS4ERR_DELAY")
Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfsd/nfs4idmap.c | 48 +++++++++++++++++++++++++++++++++++++++------
fs/nfsd/nfs4proc.c | 2 --
fs/nfsd/nfs4xdr.c | 16 +++++++++++++++
3 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/fs/nfsd/nfs4idmap.c b/fs/nfsd/nfs4idmap.c
index 717e400b16b86..21e5b4c990ef3 100644
--- a/fs/nfsd/nfs4idmap.c
+++ b/fs/nfsd/nfs4idmap.c
@@ -643,13 +643,31 @@ static __be32 encode_name_from_id(struct xdr_stream *xdr,
return idmap_id_to_name(xdr, rqstp, type, id);
}

-__be32
-nfsd_map_name_to_uid(struct svc_rqst *rqstp, const char *name, size_t namelen,
- kuid_t *uid)
+/**
+ * nfsd_map_name_to_uid - Map user@domain to local UID
+ * @rqstp: RPC execution context
+ * @name: user@domain name to be mapped
+ * @namelen: length of name, in bytes
+ * @uid: OUT: mapped local UID value
+ *
+ * Returns nfs_ok on success or an NFSv4 status code on failure.
+ */
+__be32 nfsd_map_name_to_uid(struct svc_rqst *rqstp, const char *name,
+ size_t namelen, kuid_t *uid)
{
__be32 status;
u32 id = -1;

+ /*
+ * The idmap lookup below triggers an upcall that invokes
+ * cache_check(). RQ_USEDEFERRAL must be clear to prevent
+ * cache_check() from setting RQ_DROPME via svc_defer().
+ * NFSv4 servers are not permitted to drop requests. Also
+ * RQ_DROPME will force NFSv4.1 session slot processing to
+ * be skipped.
+ */
+ WARN_ON_ONCE(test_bit(RQ_USEDEFERRAL, &rqstp->rq_flags));
+
if (name == NULL || namelen == 0)
return nfserr_inval;

@@ -660,13 +678,31 @@ nfsd_map_name_to_uid(struct svc_rqst *rqstp, const char *name, size_t namelen,
return status;
}

-__be32
-nfsd_map_name_to_gid(struct svc_rqst *rqstp, const char *name, size_t namelen,
- kgid_t *gid)
+/**
+ * nfsd_map_name_to_gid - Map user@domain to local GID
+ * @rqstp: RPC execution context
+ * @name: user@domain name to be mapped
+ * @namelen: length of name, in bytes
+ * @gid: OUT: mapped local GID value
+ *
+ * Returns nfs_ok on success or an NFSv4 status code on failure.
+ */
+__be32 nfsd_map_name_to_gid(struct svc_rqst *rqstp, const char *name,
+ size_t namelen, kgid_t *gid)
{
__be32 status;
u32 id = -1;

+ /*
+ * The idmap lookup below triggers an upcall that invokes
+ * cache_check(). RQ_USEDEFERRAL must be clear to prevent
+ * cache_check() from setting RQ_DROPME via svc_defer().
+ * NFSv4 servers are not permitted to drop requests. Also
+ * RQ_DROPME will force NFSv4.1 session slot processing to
+ * be skipped.
+ */
+ WARN_ON_ONCE(test_bit(RQ_USEDEFERRAL, &rqstp->rq_flags));
+
if (name == NULL || namelen == 0)
return nfserr_inval;

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 2d6e88f3370bf..7a85817fa5bfe 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -2717,8 +2717,6 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
BUG_ON(cstate->replay_owner);
out:
cstate->status = status;
- /* Reset deferral mechanism for RPC deferrals */
- set_bit(RQ_USEDEFERRAL, &rqstp->rq_flags);
return rpc_success;
}

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 9e25079804732..46a7fd731ba0a 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -5500,6 +5500,22 @@ nfs4svc_decode_compoundargs(struct svc_rqst *rqstp, struct xdr_stream *xdr)
args->ops = args->iops;
args->rqstp = rqstp;

+ /*
+ * NFSv4 operation decoders can invoke svc cache lookups
+ * that trigger svc_defer() when RQ_USEDEFERRAL is set,
+ * setting RQ_DROPME. This creates two problems:
+ *
+ * 1. Non-idempotency: Compounds make it too hard to avoid
+ * problems if a request is deferred and replayed.
+ *
+ * 2. Session slot leakage (NFSv4.1+): If RQ_DROPME is set
+ * during decode but SEQUENCE executes successfully, the
+ * session slot will be marked INUSE. The request is then
+ * dropped before encoding, so the slot is never released,
+ * rendering it permanently unusable by the client.
+ */
+ clear_bit(RQ_USEDEFERRAL, &rqstp->rq_flags);
+
return nfsd4_decode_compound(args);
}

--
2.51.0