Re: [PATCH] filelock: don't do security checks on nfsd setlease calls

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On Tue, 2024-02-06 at 06:59 +1100, NeilBrown wrote:
> On Mon, 05 Feb 2024, Jeff Layton wrote:
> > Zdenek reported seeing some AVC denials due to nfsd trying to set
> > delegations:
> > 
> >     type=AVC msg=audit(09.11.2023 09:03:46.411:496) : avc:  denied  { lease } for  pid=5127 comm=rpc.nfsd capability=lease  scontext=system_u:system_r:nfsd_t:s0 tcontext=system_u:system_r:nfsd_t:s0 tclass=capability permissive=0
> > 
> > When setting delegations on behalf of nfsd, we don't want to do all of
> > the normal capabilty and LSM checks. nfsd is a kernel thread and runs
> > with CAP_LEASE set, so the uid checks end up being a no-op in most cases
> > anyway.
> > 
> > Some nfsd functions can end up running in normal process context when
> > tearing down the server. At that point, the CAP_LEASE check can fail and
> > cause the client to not tear down delegations when expected.
> > 
> > Also, the way the per-fs ->setlease handlers work today is a little
> > convoluted. The non-trivial ones are wrappers around generic_setlease,
> > so when they fail due to permission problems they usually they end up
> > doing a little extra work only to determine that they can't set the
> > lease anyway. It would be more efficient to do those checks earlier.
> > 
> > Transplant the permission checking from generic_setlease to
> > vfs_setlease, which will make the permission checking happen earlier on
> > filesystems that have a ->setlease operation. Add a new kernel_setlease
> > function that bypasses these checks, and switch nfsd to use that instead
> > of vfs_setlease.
> > 
> > There is one behavioral change here: prior this patch the
> > setlease_notifier would fire even if the lease attempt was going to fail
> > the security checks later. With this change, it doesn't fire until the
> > caller has passed them. I think this is a desirable change overall. nfsd
> > is the only user of the setlease_notifier and it doesn't benefit from
> > being notified about failed attempts.
> > 
> > Cc: Ondrej Mosnáček <omosnacek@xxxxxxxxx>
> > Reported-by: Zdenek Pytela <zpytela@xxxxxxxxxx>
> > Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2248830
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> 
> Reviewed-by: NeilBrown <neilb@xxxxxxx>
> 
> It definitely nice to move all the security and sanity check early.
> This patch allows a minor clean-up in cifs which could possibly be
> included:
> diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
> index 2a4a4e3a8751..0f142d1ec64f 100644
> 
> --- a/fs/smb/client/cifsfs.c
> +++ b/fs/smb/client/cifsfs.c
> @@ -1094,9 +1094,6 @@ cifs_setlease(struct file *file, int arg, struct file_lock **lease, void **priv)
>  	struct inode *inode = file_inode(file);
>  	struct cifsFileInfo *cfile = file->private_data;
>  
> -	if (!(S_ISREG(inode->i_mode)))
> -		return -EINVAL;
> -
>  	/* Check if file is oplocked if this is request for new lease */
>  	if (arg == F_UNLCK ||
>  	    ((arg == F_RDLCK) && CIFS_CACHE_READ(CIFS_I(inode))) ||
> 
> 
> as ->setlease() is now never called for non-ISREG files.
> 
> NeilBrown
> 
> 

Ahh yeah. Good point. I'm fine with including that if Christian wants to
fold it in.

Thanks for the review!


> > ---
> > This patch is based on top of a merge of Christian's vfs.file branch
> > (which has the file_lock/lease split). There is a small merge confict
> > with Chuck's nfsd-next patch, but it should be fairly simple to resolve.
> > ---
> >  fs/locks.c               | 43 +++++++++++++++++++++++++------------------
> >  fs/nfsd/nfs4layouts.c    |  5 ++---
> >  fs/nfsd/nfs4state.c      |  8 ++++----
> >  include/linux/filelock.h |  7 +++++++
> >  4 files changed, 38 insertions(+), 25 deletions(-)
> > 
> > diff --git a/fs/locks.c b/fs/locks.c
> > index 33c7f4a8c729..26d52ef5314a 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -1925,18 +1925,6 @@ static int generic_delete_lease(struct file *filp, void *owner)
> >  int generic_setlease(struct file *filp, int arg, struct file_lease **flp,
> >  			void **priv)
> >  {
> > -	struct inode *inode = file_inode(filp);
> > -	vfsuid_t vfsuid = i_uid_into_vfsuid(file_mnt_idmap(filp), inode);
> > -	int error;
> > -
> > -	if ((!vfsuid_eq_kuid(vfsuid, current_fsuid())) && !capable(CAP_LEASE))
> > -		return -EACCES;
> > -	if (!S_ISREG(inode->i_mode))
> > -		return -EINVAL;
> > -	error = security_file_lock(filp, arg);
> > -	if (error)
> > -		return error;
> > -
> >  	switch (arg) {
> >  	case F_UNLCK:
> >  		return generic_delete_lease(filp, *priv);
> > @@ -1987,6 +1975,19 @@ void lease_unregister_notifier(struct notifier_block *nb)
> >  }
> >  EXPORT_SYMBOL_GPL(lease_unregister_notifier);
> >  
> > +
> > +int
> > +kernel_setlease(struct file *filp, int arg, struct file_lease **lease, void **priv)
> > +{
> > +	if (lease)
> > +		setlease_notifier(arg, *lease);
> > +	if (filp->f_op->setlease)
> > +		return filp->f_op->setlease(filp, arg, lease, priv);
> > +	else
> > +		return generic_setlease(filp, arg, lease, priv);
> > +}
> > +EXPORT_SYMBOL_GPL(kernel_setlease);
> > +
> >  /**
> >   * vfs_setlease        -       sets a lease on an open file
> >   * @filp:	file pointer
> > @@ -2007,12 +2008,18 @@ EXPORT_SYMBOL_GPL(lease_unregister_notifier);
> >  int
> >  vfs_setlease(struct file *filp, int arg, struct file_lease **lease, void **priv)
> >  {
> > -	if (lease)
> > -		setlease_notifier(arg, *lease);
> > -	if (filp->f_op->setlease)
> > -		return filp->f_op->setlease(filp, arg, lease, priv);
> > -	else
> > -		return generic_setlease(filp, arg, lease, priv);
> > +	struct inode *inode = file_inode(filp);
> > +	vfsuid_t vfsuid = i_uid_into_vfsuid(file_mnt_idmap(filp), inode);
> > +	int error;
> > +
> > +	if ((!vfsuid_eq_kuid(vfsuid, current_fsuid())) && !capable(CAP_LEASE))
> > +		return -EACCES;
> > +	if (!S_ISREG(inode->i_mode))
> > +		return -EINVAL;
> > +	error = security_file_lock(filp, arg);
> > +	if (error)
> > +		return error;
> > +	return kernel_setlease(filp, arg, lease, priv);
> >  }
> >  EXPORT_SYMBOL_GPL(vfs_setlease);
> >  
> > diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
> > index 4fa21b74a981..4c0d00bdfbb1 100644
> > --- a/fs/nfsd/nfs4layouts.c
> > +++ b/fs/nfsd/nfs4layouts.c
> > @@ -170,7 +170,7 @@ nfsd4_free_layout_stateid(struct nfs4_stid *stid)
> >  	spin_unlock(&fp->fi_lock);
> >  
> >  	if (!nfsd4_layout_ops[ls->ls_layout_type]->disable_recalls)
> > -		vfs_setlease(ls->ls_file->nf_file, F_UNLCK, NULL, (void **)&ls);
> > +		kernel_setlease(ls->ls_file->nf_file, F_UNLCK, NULL, (void **)&ls);
> >  	nfsd_file_put(ls->ls_file);
> >  
> >  	if (ls->ls_recalled)
> > @@ -199,8 +199,7 @@ nfsd4_layout_setlease(struct nfs4_layout_stateid *ls)
> >  	fl->c.flc_pid = current->tgid;
> >  	fl->c.flc_file = ls->ls_file->nf_file;
> >  
> > -	status = vfs_setlease(fl->c.flc_file, fl->c.flc_type, &fl,
> > -			      NULL);
> > +	status = kernel_setlease(fl->c.flc_file, fl->c.flc_type, &fl, NULL);
> >  	if (status) {
> >  		locks_free_lease(fl);
> >  		return status;
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index b2c8efb5f793..6d52ecba8e9c 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -1249,7 +1249,7 @@ static void nfs4_unlock_deleg_lease(struct nfs4_delegation *dp)
> >  
> >  	WARN_ON_ONCE(!fp->fi_delegees);
> >  
> > -	vfs_setlease(nf->nf_file, F_UNLCK, NULL, (void **)&dp);
> > +	kernel_setlease(nf->nf_file, F_UNLCK, NULL, (void **)&dp);
> >  	put_deleg_file(fp);
> >  }
> >  
> > @@ -5532,8 +5532,8 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> >  	if (!fl)
> >  		goto out_clnt_odstate;
> >  
> > -	status = vfs_setlease(fp->fi_deleg_file->nf_file,
> > -			      fl->c.flc_type, &fl, NULL);
> > +	status = kernel_setlease(fp->fi_deleg_file->nf_file,
> > +				      fl->c.flc_type, &fl, NULL);
> >  	if (fl)
> >  		locks_free_lease(fl);
> >  	if (status)
> > @@ -5571,7 +5571,7 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> >  
> >  	return dp;
> >  out_unlock:
> > -	vfs_setlease(fp->fi_deleg_file->nf_file, F_UNLCK, NULL, (void **)&dp);
> > +	kernel_setlease(fp->fi_deleg_file->nf_file, F_UNLCK, NULL, (void **)&dp);
> >  out_clnt_odstate:
> >  	put_clnt_odstate(dp->dl_clnt_odstate);
> >  	nfs4_put_stid(&dp->dl_stid);
> > diff --git a/include/linux/filelock.h b/include/linux/filelock.h
> > index 4a5ad26962c1..cd6c1c291de9 100644
> > --- a/include/linux/filelock.h
> > +++ b/include/linux/filelock.h
> > @@ -208,6 +208,7 @@ struct file_lease *locks_alloc_lease(void);
> >  int __break_lease(struct inode *inode, unsigned int flags, unsigned int type);
> >  void lease_get_mtime(struct inode *, struct timespec64 *time);
> >  int generic_setlease(struct file *, int, struct file_lease **, void **priv);
> > +int kernel_setlease(struct file *, int, struct file_lease **, void **);
> >  int vfs_setlease(struct file *, int, struct file_lease **, void **);
> >  int lease_modify(struct file_lease *, int, struct list_head *);
> >  
> > @@ -357,6 +358,12 @@ static inline int generic_setlease(struct file *filp, int arg,
> >  	return -EINVAL;
> >  }
> >  
> > +static inline int kernel_setlease(struct file *filp, int arg,
> > +			       struct file_lease **lease, void **priv)
> > +{
> > +	return -EINVAL;
> > +}
> > +
> >  static inline int vfs_setlease(struct file *filp, int arg,
> >  			       struct file_lease **lease, void **priv)
> >  {
> > 
> > ---
> > base-commit: 1499e59af376949b062cdc039257f811f6c1697f
> > change-id: 20240202-bz2248830-03e6c7506705
> > 
> > Best regards,
> > -- 
> > Jeff Layton <jlayton@xxxxxxxxxx>
> > 
> > 
> > 
> 

-- 
Jeff Layton <jlayton@xxxxxxxxxx>





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