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filelock: don't do security checks on nfsd setlease calls

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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@gmail.com>
Reported-by: Zdenek Pytela <zpytela@redhat.com>
Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2248830
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20240205-bz2248830-v1-1-d0ec0daecba1@kernel.org
Acked-by: Tom Talpey <tom@talpey.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Jeff Layton 2024-02-05 07:09:31 -05:00 committed by Christian Brauner
parent c4b3ffb508
commit 7b8001013d
4 changed files with 38 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
fs/locks.c
View File

@ -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);

5
fs/nfsd/nfs4layouts.c
View File

@ -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;

8
fs/nfsd/nfs4state.c
View File

@ -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);

7
include/linux/filelock.h
View File

@ -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 *);
@ -378,6 +379,12 @@ 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)
{