5.15-stable review patch. If anyone has any objections, please let me know.
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From: Chuck Lever chuck.lever@oracle.com
[ 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@oracle.com --- 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)