Re: [PATCH] filelock: don't do security checks on nfsd setlease calls
From: Tom Talpey
Date: Mon Feb 05 2024 - 17:23:44 EST
On 2/5/2024 3:16 PM, Jeff Layton wrote:
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!
[re-replying to fix cc linux-cifs@ /vger/. kernel.org ...]
cifsfs.c is a new file being added to the change, cc-ing linux-cifs
for awareness. The SMB3 protocol does support leases on directories, so
this vfs change might be important to note in the future.
In the meantime, for cifsfs.c:
Acked-by: Tom Talpey <tom@xxxxxxxxxx>
Tom.
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>