5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chuck Lever <chuck.lever@xxxxxxxxxx>
[ Upstream commit 91d2e9b56cf5c80f9efc530d494968369a8a0e0d ]
There are two boot-time fields in struct nfsd_net: one called
boot_time and one called nfssvc_boot. The latter is used only to
form write verifiers, but its documenting comment declares:
/* Time of server startup */
Since commit 27c438f53e79 ("nfsd: Support the server resetting the
boot verifier"), this field can be reset at any time; it's no
longer tied to server restart. So that comment is stale.
Also, according to pahole, struct timespec64 is 16 bytes long on
x86_64. The nfssvc_boot field is used only to form a write verifier,
which is 8 bytes long.
Let's clarify this situation by manufacturing an 8-byte verifier
in nfs_reset_boot_verifier() and storing only that in struct
nfsd_net.
We're grabbing 128 bits of time, so compress all of those into a
64-bit verifier instead of throwing out the high-order bits.
In the future, the siphash_key can be re-used for other hashed
objects per-nfsd_net.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
fs/nfsd/netns.h | 8 +++++---
fs/nfsd/nfsctl.c | 3 ++-
fs/nfsd/nfssvc.c | 51 ++++++++++++++++++++++++++++++++++++------------
3 files changed, 45 insertions(+), 17 deletions(-)
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 9e8b77d2a3a47..a6ed300259849 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -11,6 +11,7 @@
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <linux/percpu_counter.h>
+#include <linux/siphash.h>
/* Hash tables for nfs4_clientid state */
#define CLIENT_HASH_BITS 4
@@ -108,9 +109,8 @@ struct nfsd_net {
bool nfsd_net_up;
bool lockd_up;
- /* Time of server startup */
- struct timespec64 nfssvc_boot;
- seqlock_t boot_lock;
+ seqlock_t writeverf_lock;
+ unsigned char writeverf[8];
/*
* Max number of connections this nfsd container will allow. Defaults
@@ -187,6 +187,8 @@ struct nfsd_net {
char nfsd_name[UNX_MAXNODENAME+1];
struct nfsd_fcache_disposal *fcache_disposal;
+
+ siphash_key_t siphash_key;
};
/* Simple check to find out if a given net was properly initialized */
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 504b169d27881..68b020f2002b7 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1484,7 +1484,8 @@ static __net_init int nfsd_init_net(struct net *net)
nn->clientid_counter = nn->clientid_base + 1;
nn->s2s_cp_cl_id = nn->clientid_counter++;
- seqlock_init(&nn->boot_lock);
+ get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
+ seqlock_init(&nn->writeverf_lock);
return 0;
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 4d1d8aa6d7f9d..5a60664695352 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -12,6 +12,7 @@
#include <linux/module.h>
#include <linux/fs_struct.h>
#include <linux/swap.h>
+#include <linux/siphash.h>
#include <linux/sunrpc/stats.h>
#include <linux/sunrpc/svcsock.h>
@@ -344,33 +345,57 @@ static bool nfsd_needs_lockd(struct nfsd_net *nn)
return nfsd_vers(nn, 2, NFSD_TEST) || nfsd_vers(nn, 3, NFSD_TEST);
}
+/**
+ * nfsd_copy_boot_verifier - Atomically copy a write verifier
+ * @verf: buffer in which to receive the verifier cookie
+ * @nn: NFS net namespace
+ *
+ * This function provides a wait-free mechanism for copying the
+ * namespace's boot verifier without tearing it.
+ */
void nfsd_copy_boot_verifier(__be32 verf[2], struct nfsd_net *nn)
{
int seq = 0;
do {
- read_seqbegin_or_lock(&nn->boot_lock, &seq);
- /*
- * This is opaque to client, so no need to byte-swap. Use
- * __force to keep sparse happy. y2038 time_t overflow is
- * irrelevant in this usage
- */
- verf[0] = (__force __be32)nn->nfssvc_boot.tv_sec;
- verf[1] = (__force __be32)nn->nfssvc_boot.tv_nsec;
- } while (need_seqretry(&nn->boot_lock, seq));
- done_seqretry(&nn->boot_lock, seq);
+ read_seqbegin_or_lock(&nn->writeverf_lock, &seq);
+ memcpy(verf, nn->writeverf, sizeof(*verf));
+ } while (need_seqretry(&nn->writeverf_lock, seq));
+ done_seqretry(&nn->writeverf_lock, seq);
}
static void nfsd_reset_boot_verifier_locked(struct nfsd_net *nn)
{
- ktime_get_raw_ts64(&nn->nfssvc_boot);
+ struct timespec64 now;
+ u64 verf;
+
+ /*
+ * Because the time value is hashed, y2038 time_t overflow
+ * is irrelevant in this usage.
+ */
+ ktime_get_raw_ts64(&now);
+ verf = siphash_2u64(now.tv_sec, now.tv_nsec, &nn->siphash_key);
+ memcpy(nn->writeverf, &verf, sizeof(nn->writeverf));
}
+/**
+ * nfsd_reset_boot_verifier - Generate a new boot verifier
+ * @nn: NFS net namespace
+ *
+ * This function updates the ->writeverf field of @nn. This field
+ * contains an opaque cookie that, according to Section 18.32.3 of
+ * RFC 8881, "the client can use to determine whether a server has
+ * changed instance state (e.g., server restart) between a call to
+ * WRITE and a subsequent call to either WRITE or COMMIT. This
+ * cookie MUST be unchanged during a single instance of the NFSv4.1
+ * server and MUST be unique between instances of the NFSv4.1
+ * server."
+ */
void nfsd_reset_boot_verifier(struct nfsd_net *nn)
{
- write_seqlock(&nn->boot_lock);
+ write_seqlock(&nn->writeverf_lock);
nfsd_reset_boot_verifier_locked(nn);
- write_sequnlock(&nn->boot_lock);
+ write_sequnlock(&nn->writeverf_lock);
}
static int nfsd_startup_net(struct net *net, const struct cred *cred)
--
2.43.0
