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nfsd: disallow file locking and delegations for NFSv4 reexport

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We do not and cannot support file locking with NFS reexport over
NFSv4.x for the same reason we don't do it for NFSv3: NFS reexport
server reboot cannot allow clients to recover locks because the source
NFS server has not rebooted, and so it is not in grace.  Since the
source NFS server is not in grace, it cannot offer any guarantees that
the file won't have been changed between the locks getting lost and
any attempt to recover/reclaim them.  The same applies to delegations
and any associated locks, so disallow them too.

Clients are no longer allowed to get file locks or delegations from a
reexport server, any attempts will fail with operation not supported.

Update the "Reboot recovery" section accordingly in
Documentation/filesystems/nfs/reexport.rst

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Mike Snitzer 2025-02-10 11:25:53 -05:00 committed by Chuck Lever
parent fbfdc9fc0f
commit 9254c8ae9b
4 changed files with 40 additions and 5 deletions
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10
Documentation/filesystems/nfs/reexport.rst
View File

@ -26,9 +26,13 @@ Reboot recovery
---------------
The NFS protocol's normal reboot recovery mechanisms don't work for the
case when the reexport server reboots. Clients will lose any locks
they held before the reboot, and further IO will result in errors.
Closing and reopening files should clear the errors.
case when the reexport server reboots because the source server has not
rebooted, and so it is not in grace. Since the source server is not in
grace, it cannot offer any guarantees that the file won't have been
changed between the locks getting lost and any attempt to recover them.
The same applies to delegations and any associated locks. Clients are
not allowed to get file locks or delegations from a reexport server, any
attempts will fail with operation not supported.
Filehandle limits
-----------------

3
fs/nfs/export.c
View File

@ -154,5 +154,6 @@ const struct export_operations nfs_export_ops = {
EXPORT_OP_CLOSE_BEFORE_UNLINK |
EXPORT_OP_REMOTE_FS |
EXPORT_OP_NOATOMIC_ATTR |
EXPORT_OP_FLUSH_ON_CLOSE,
EXPORT_OP_FLUSH_ON_CLOSE |
EXPORT_OP_NOLOCKS,
};

18
fs/nfsd/nfs4state.c
View File

@ -6010,6 +6010,15 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
if (!nf)
return ERR_PTR(-EAGAIN);
/*
* File delegations and associated locks cannot be recovered if the
* export is from an NFS proxy server.
*/
if (exportfs_cannot_lock(nf->nf_file->f_path.mnt->mnt_sb->s_export_op)) {
nfsd_file_put(nf);
return ERR_PTR(-EOPNOTSUPP);
}
spin_lock(&state_lock);
spin_lock(&fp->fi_lock);
if (nfs4_delegation_exists(clp, fp))
@ -8148,6 +8157,10 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
status = fh_verify(rqstp, &cstate->current_fh, S_IFREG, 0);
if (status != nfs_ok)
return status;
if (exportfs_cannot_lock(cstate->current_fh.fh_dentry->d_sb->s_export_op)) {
status = nfserr_notsupp;
goto out;
}
if (lock->lk_is_new) {
if (nfsd4_has_session(cstate))
@ -8487,6 +8500,11 @@ nfsd4_locku(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
status = nfserr_lock_range;
goto put_stateid;
}
if (exportfs_cannot_lock(nf->nf_file->f_path.mnt->mnt_sb->s_export_op)) {
status = nfserr_notsupp;
goto put_file;
}
file_lock = locks_alloc_lock();
if (!file_lock) {
dprintk("NFSD: %s: unable to allocate lock!\n", __func__);

14
include/linux/exportfs.h
View File

@ -279,10 +279,22 @@ struct export_operations {
atomic attribute updates
*/
#define EXPORT_OP_FLUSH_ON_CLOSE (0x20) /* fs flushes file data on close */
#define EXPORT_OP_ASYNC_LOCK (0x40) /* fs can do async lock request */
#define EXPORT_OP_NOLOCKS (0x40) /* no file locking support */
unsigned long flags;
};
/**
* exportfs_cannot_lock() - check if export implements file locking
* @export_ops: the nfs export operations to check
*
* Returns true if the export does not support file locking.
*/
static inline bool
exportfs_cannot_lock(const struct export_operations *export_ops)
{
return export_ops->flags & EXPORT_OP_NOLOCKS;
}
extern int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
int *max_len, struct inode *parent,
int flags);