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Message-ID: <cd3f8b0d2d0c0a58472b9a83b9c89dbbc6ad4e5c.camel@kernel.org>
Date: Mon, 05 Feb 2024 15:16:15 -0500
From: Jeff Layton <jlayton@...nel.org>
To: NeilBrown <neilb@...e.de>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner
<brauner@...nel.org>, Jan Kara <jack@...e.cz>, Chuck Lever
<chuck.lever@...cle.com>, Olga Kornievskaia <kolga@...app.com>, Dai Ngo
<Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-nfs@...r.kernel.org, Ondrej Mosnáček
<omosnacek@...il.com>, Zdenek Pytela <zpytela@...hat.com>
Subject: Re: [PATCH] filelock: don't do security checks on nfsd setlease
calls
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@...il.com>
> > Reported-by: Zdenek Pytela <zpytela@...hat.com>
> > Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2248830
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
>
> Reviewed-by: NeilBrown <neilb@...e.de>
>
> 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@...nel.org>
> >
> >
> >
>
--
Jeff Layton <jlayton@...nel.org>
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