Writing to v4_end_grace can race with server shutdown and result in memory being accessed after it was freed - reclaim_str_hashtbl in particular. We cannot hold nfsd_mutex across the nfsd4_end_grace() call as that is held while client_tracking_op->init() is called and that can wait for an upcall to nfsdcltrack which can write to v4_end_grace, resulting in a deadlock. nfsd4_end_grace() is also called by the landromat work queue and this doesn't require locking as server shutdown will stop the work and wait for it before freeing anything that nfsd4_end_grace() might access. However, we must be sure that writing to v4_end_grace doesn't restart the work item after shutdown has already waited for it. For this we add a new flag protected with a spin_lock, and nn->client_lock is suitable. It is set only while it is safe to make client tracking calls, and v4_end_grace only schedules work while the flag is set and with the spin_lock held. So this patch adds an nfsd_net field "client_tracking_active" which is set as described. Another field "grace_end_forced", is set when v4_end_grace is written. After this is set, and providing client_tracking_active is set, the laundromat is scheduled. This "grace_end_forced" field bypasses other checks for whether the grace period has finished. This resolves a race which can result in use-after-free. Reported-and-tested-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx> Closes: https://lore.kernel.org/linux-nfs/20250513074305.3362209-1-lilingfeng3@xxxxxxxxxx Fixes: 7f5ef2e900d9 ("nfsd: add a v4_end_grace file to /proc/fs/nfsd") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: NeilBrown <neil@xxxxxxxxxx> --- fs/nfsd/netns.h | 2 ++ fs/nfsd/nfs4state.c | 45 +++++++++++++++++++++++++++++++++++++++++++-- fs/nfsd/nfsctl.c | 6 +++--- fs/nfsd/state.h | 2 +- 4 files changed, 49 insertions(+), 6 deletions(-) diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h index 3e2d0fde80a7..fe8338735e7c 100644 --- a/fs/nfsd/netns.h +++ b/fs/nfsd/netns.h @@ -66,6 +66,8 @@ struct nfsd_net { struct lock_manager nfsd4_manager; bool grace_ended; + bool grace_end_forced; + bool client_tracking_active; time64_t boot_time; struct dentry *nfsd_client_dir; diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index d5694987f86f..124fe4f669aa 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -84,7 +84,7 @@ static u64 current_sessionid = 1; /* forward declarations */ static bool check_for_locks(struct nfs4_file *fp, struct nfs4_lockowner *lowner); static void nfs4_free_ol_stateid(struct nfs4_stid *stid); -void nfsd4_end_grace(struct nfsd_net *nn); +static void nfsd4_end_grace(struct nfsd_net *nn); static void _free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cpntf_state *cps); static void nfsd4_file_hash_remove(struct nfs4_file *fi); static void deleg_reaper(struct nfsd_net *nn); @@ -6458,7 +6458,7 @@ nfsd4_renew(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, return nfs_ok; } -void +static void nfsd4_end_grace(struct nfsd_net *nn) { /* do nothing if grace period already ended */ @@ -6491,6 +6491,36 @@ nfsd4_end_grace(struct nfsd_net *nn) */ } +/** + * nfsd4_force_end_grace - forcibly end the grace period + * @nn: nfsd_net in which the grace period must end. + * + * + * An nfsv4 grace period can be terminated early if it is known that + * no more client could reclaim state. Sometimes user-space can provide + * that information - which will potentially be provided asychnronously + * w.r.t. server startup or shutdown. + * + * nfsd4_force_end_grace() causing the grace period to end and takes + * care to ensure races with server start/stop are not problematic. + * + * Return value: %false if the NFS server was not active and + * %true if the server was, or may have been, active. + */ +bool +nfsd4_force_end_grace(struct nfsd_net *nn) +{ + if (!nn->client_tracking_ops) + return false; + spin_lock(&nn->client_lock); + if (nn->client_tracking_active) { + nn->grace_end_forced = true; + mod_delayed_work(laundry_wq, &nn->laundromat_work, 0); + } + spin_unlock(&nn->client_lock); + return true; +} + /* * If we've waited a lease period but there are still clients trying to * reclaim, wait a little longer to give them a chance to finish. @@ -6500,6 +6530,8 @@ static bool clients_still_reclaiming(struct nfsd_net *nn) time64_t double_grace_period_end = nn->boot_time + 2 * nn->nfsd4_lease; + if (nn->grace_end_forced) + return false; if (nn->track_reclaim_completes && atomic_read(&nn->nr_reclaim_complete) == nn->reclaim_str_hashtbl_size) @@ -8807,6 +8839,8 @@ static int nfs4_state_create_net(struct net *net) nn->unconf_name_tree = RB_ROOT; nn->boot_time = ktime_get_real_seconds(); nn->grace_ended = false; + nn->grace_end_forced = false; + nn->client_tracking_active = false; nn->nfsd4_manager.block_opens = true; INIT_LIST_HEAD(&nn->nfsd4_manager.list); INIT_LIST_HEAD(&nn->client_lru); @@ -8887,6 +8921,10 @@ nfs4_state_start_net(struct net *net) return ret; locks_start_grace(net, &nn->nfsd4_manager); nfsd4_client_tracking_init(net); + /* safe for laundromat to run now */ + spin_lock(&nn->client_lock); + nn->client_tracking_active = true; + spin_unlock(&nn->client_lock); if (nn->track_reclaim_completes && nn->reclaim_str_hashtbl_size == 0) goto skip_grace; printk(KERN_INFO "NFSD: starting %lld-second grace period (net %x)\n", @@ -8935,6 +8973,9 @@ nfs4_state_shutdown_net(struct net *net) shrinker_free(nn->nfsd_client_shrinker); cancel_work_sync(&nn->nfsd_shrinker_work); + spin_lock(&nn->client_lock); + nn->client_tracking_active = false; + spin_unlock(&nn->client_lock); cancel_delayed_work_sync(&nn->laundromat_work); locks_end_grace(&nn->nfsd4_manager); diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c index 3f3e9f6c4250..658f3f86a59f 100644 --- a/fs/nfsd/nfsctl.c +++ b/fs/nfsd/nfsctl.c @@ -1082,10 +1082,10 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size) case 'Y': case 'y': case '1': - if (!nn->nfsd_serv) - return -EBUSY; trace_nfsd_end_grace(netns(file)); - nfsd4_end_grace(nn); + if (!nfsd4_force_end_grace(nn)) + return -EBUSY; + break; default: return -EINVAL; diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h index 1995bca158b8..05eabc69de40 100644 --- a/fs/nfsd/state.h +++ b/fs/nfsd/state.h @@ -836,7 +836,7 @@ static inline void nfsd4_revoke_states(struct net *net, struct super_block *sb) #endif /* grace period management */ -void nfsd4_end_grace(struct nfsd_net *nn); +bool nfsd4_force_end_grace(struct nfsd_net *nn); /* nfs4recover operations */ extern int nfsd4_client_tracking_init(struct net *net); -- 2.49.0
