linux/fs/nfs/nfs3acl.c
Christian Brauner cac2f8b8d8
fs: rename current get acl method
The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

The current inode operation for getting posix acls takes an inode
argument but various filesystems (e.g., 9p, cifs, overlayfs) need access
to the dentry. In contrast to the ->set_acl() inode operation we cannot
simply extend ->get_acl() to take a dentry argument. The ->get_acl()
inode operation is called from:

acl_permission_check()
-> check_acl()
   -> get_acl()

which is part of generic_permission() which in turn is part of
inode_permission(). Both generic_permission() and inode_permission() are
called in the ->permission() handler of various filesystems (e.g.,
overlayfs). So simply passing a dentry argument to ->get_acl() would
amount to also having to pass a dentry argument to ->permission(). We
should avoid this unnecessary change.

So instead of extending the existing inode operation rename it from
->get_acl() to ->get_inode_acl() and add a ->get_acl() method later that
passes a dentry argument and which filesystems that need access to the
dentry can implement instead of ->get_inode_acl(). Filesystems like cifs
which allow setting and getting posix acls but not using them for
permission checking during lookup can simply not implement
->get_inode_acl().

This is intended to be a non-functional change.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Suggested-by/Inspired-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-10-20 10:13:27 +02:00

351 lines
8.2 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/nfs.h>
#include <linux/nfs3.h>
#include <linux/nfs_fs.h>
#include <linux/posix_acl_xattr.h>
#include <linux/nfsacl.h>
#include "internal.h"
#include "nfs3_fs.h"
#define NFSDBG_FACILITY NFSDBG_PROC
/*
* nfs3_prepare_get_acl, nfs3_complete_get_acl, nfs3_abort_get_acl: Helpers for
* caching get_acl results in a race-free way. See fs/posix_acl.c:get_acl()
* for explanations.
*/
static void nfs3_prepare_get_acl(struct posix_acl **p)
{
struct posix_acl *sentinel = uncached_acl_sentinel(current);
if (cmpxchg(p, ACL_NOT_CACHED, sentinel) != ACL_NOT_CACHED) {
/* Not the first reader or sentinel already in place. */
}
}
static void nfs3_complete_get_acl(struct posix_acl **p, struct posix_acl *acl)
{
struct posix_acl *sentinel = uncached_acl_sentinel(current);
/* Only cache the ACL if our sentinel is still in place. */
posix_acl_dup(acl);
if (cmpxchg(p, sentinel, acl) != sentinel)
posix_acl_release(acl);
}
static void nfs3_abort_get_acl(struct posix_acl **p)
{
struct posix_acl *sentinel = uncached_acl_sentinel(current);
/* Remove our sentinel upon failure. */
cmpxchg(p, sentinel, ACL_NOT_CACHED);
}
struct posix_acl *nfs3_get_acl(struct inode *inode, int type, bool rcu)
{
struct nfs_server *server = NFS_SERVER(inode);
struct page *pages[NFSACL_MAXPAGES] = { };
struct nfs3_getaclargs args = {
.fh = NFS_FH(inode),
/* The xdr layer may allocate pages here. */
.pages = pages,
};
struct nfs3_getaclres res = {
NULL,
};
struct rpc_message msg = {
.rpc_argp = &args,
.rpc_resp = &res,
};
int status, count;
if (rcu)
return ERR_PTR(-ECHILD);
if (!nfs_server_capable(inode, NFS_CAP_ACLS))
return ERR_PTR(-EOPNOTSUPP);
status = nfs_revalidate_inode(inode, NFS_INO_INVALID_CHANGE);
if (status < 0)
return ERR_PTR(status);
/*
* Only get the access acl when explicitly requested: We don't
* need it for access decisions, and only some applications use
* it. Applications which request the access acl first are not
* penalized from this optimization.
*/
if (type == ACL_TYPE_ACCESS)
args.mask |= NFS_ACLCNT|NFS_ACL;
if (S_ISDIR(inode->i_mode))
args.mask |= NFS_DFACLCNT|NFS_DFACL;
if (args.mask == 0)
return NULL;
dprintk("NFS call getacl\n");
msg.rpc_proc = &server->client_acl->cl_procinfo[ACLPROC3_GETACL];
res.fattr = nfs_alloc_fattr();
if (res.fattr == NULL)
return ERR_PTR(-ENOMEM);
if (args.mask & NFS_ACL)
nfs3_prepare_get_acl(&inode->i_acl);
if (args.mask & NFS_DFACL)
nfs3_prepare_get_acl(&inode->i_default_acl);
status = rpc_call_sync(server->client_acl, &msg, 0);
dprintk("NFS reply getacl: %d\n", status);
/* pages may have been allocated at the xdr layer. */
for (count = 0; count < NFSACL_MAXPAGES && args.pages[count]; count++)
__free_page(args.pages[count]);
switch (status) {
case 0:
status = nfs_refresh_inode(inode, res.fattr);
break;
case -EPFNOSUPPORT:
case -EPROTONOSUPPORT:
dprintk("NFS_V3_ACL extension not supported; disabling\n");
server->caps &= ~NFS_CAP_ACLS;
fallthrough;
case -ENOTSUPP:
status = -EOPNOTSUPP;
goto getout;
default:
goto getout;
}
if ((args.mask & res.mask) != args.mask) {
status = -EIO;
goto getout;
}
if (res.acl_access != NULL) {
if ((posix_acl_equiv_mode(res.acl_access, NULL) == 0) ||
res.acl_access->a_count == 0) {
posix_acl_release(res.acl_access);
res.acl_access = NULL;
}
}
if (res.mask & NFS_ACL)
nfs3_complete_get_acl(&inode->i_acl, res.acl_access);
else
forget_cached_acl(inode, ACL_TYPE_ACCESS);
if (res.mask & NFS_DFACL)
nfs3_complete_get_acl(&inode->i_default_acl, res.acl_default);
else
forget_cached_acl(inode, ACL_TYPE_DEFAULT);
nfs_free_fattr(res.fattr);
if (type == ACL_TYPE_ACCESS) {
posix_acl_release(res.acl_default);
return res.acl_access;
} else {
posix_acl_release(res.acl_access);
return res.acl_default;
}
getout:
nfs3_abort_get_acl(&inode->i_acl);
nfs3_abort_get_acl(&inode->i_default_acl);
posix_acl_release(res.acl_access);
posix_acl_release(res.acl_default);
nfs_free_fattr(res.fattr);
return ERR_PTR(status);
}
static int __nfs3_proc_setacls(struct inode *inode, struct posix_acl *acl,
struct posix_acl *dfacl)
{
struct nfs_server *server = NFS_SERVER(inode);
struct nfs_fattr *fattr;
struct page *pages[NFSACL_MAXPAGES];
struct nfs3_setaclargs args = {
.inode = inode,
.mask = NFS_ACL,
.acl_access = acl,
.pages = pages,
};
struct rpc_message msg = {
.rpc_argp = &args,
.rpc_resp = &fattr,
};
int status = 0;
if (acl == NULL && (!S_ISDIR(inode->i_mode) || dfacl == NULL))
goto out;
status = -EOPNOTSUPP;
if (!nfs_server_capable(inode, NFS_CAP_ACLS))
goto out;
/* We are doing this here because XDR marshalling does not
* return any results, it BUGs. */
status = -ENOSPC;
if (acl != NULL && acl->a_count > NFS_ACL_MAX_ENTRIES)
goto out;
if (dfacl != NULL && dfacl->a_count > NFS_ACL_MAX_ENTRIES)
goto out;
if (S_ISDIR(inode->i_mode)) {
args.mask |= NFS_DFACL;
args.acl_default = dfacl;
args.len = nfsacl_size(acl, dfacl);
} else
args.len = nfsacl_size(acl, NULL);
if (args.len > NFS_ACL_INLINE_BUFSIZE) {
unsigned int npages = 1 + ((args.len - 1) >> PAGE_SHIFT);
status = -ENOMEM;
do {
args.pages[args.npages] = alloc_page(GFP_KERNEL);
if (args.pages[args.npages] == NULL)
goto out_freepages;
args.npages++;
} while (args.npages < npages);
}
dprintk("NFS call setacl\n");
status = -ENOMEM;
fattr = nfs_alloc_fattr();
if (fattr == NULL)
goto out_freepages;
msg.rpc_proc = &server->client_acl->cl_procinfo[ACLPROC3_SETACL];
msg.rpc_resp = fattr;
status = rpc_call_sync(server->client_acl, &msg, 0);
nfs_access_zap_cache(inode);
nfs_zap_acl_cache(inode);
dprintk("NFS reply setacl: %d\n", status);
switch (status) {
case 0:
status = nfs_refresh_inode(inode, fattr);
break;
case -EPFNOSUPPORT:
case -EPROTONOSUPPORT:
dprintk("NFS_V3_ACL SETACL RPC not supported"
"(will not retry)\n");
server->caps &= ~NFS_CAP_ACLS;
fallthrough;
case -ENOTSUPP:
status = -EOPNOTSUPP;
}
nfs_free_fattr(fattr);
out_freepages:
while (args.npages != 0) {
args.npages--;
__free_page(args.pages[args.npages]);
}
out:
return status;
}
int nfs3_proc_setacls(struct inode *inode, struct posix_acl *acl,
struct posix_acl *dfacl)
{
int ret;
ret = __nfs3_proc_setacls(inode, acl, dfacl);
return (ret == -EOPNOTSUPP) ? 0 : ret;
}
int nfs3_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
struct posix_acl *acl, int type)
{
struct posix_acl *orig = acl, *dfacl = NULL, *alloc;
struct inode *inode = d_inode(dentry);
int status;
if (S_ISDIR(inode->i_mode)) {
switch(type) {
case ACL_TYPE_ACCESS:
alloc = get_inode_acl(inode, ACL_TYPE_DEFAULT);
if (IS_ERR(alloc))
goto fail;
dfacl = alloc;
break;
case ACL_TYPE_DEFAULT:
alloc = get_inode_acl(inode, ACL_TYPE_ACCESS);
if (IS_ERR(alloc))
goto fail;
dfacl = acl;
acl = alloc;
break;
}
}
if (acl == NULL) {
alloc = posix_acl_from_mode(inode->i_mode, GFP_KERNEL);
if (IS_ERR(alloc))
goto fail;
acl = alloc;
}
status = __nfs3_proc_setacls(inode, acl, dfacl);
out:
if (acl != orig)
posix_acl_release(acl);
if (dfacl != orig)
posix_acl_release(dfacl);
return status;
fail:
status = PTR_ERR(alloc);
goto out;
}
const struct xattr_handler *nfs3_xattr_handlers[] = {
&posix_acl_access_xattr_handler,
&posix_acl_default_xattr_handler,
NULL,
};
static int
nfs3_list_one_acl(struct inode *inode, int type, const char *name, void *data,
size_t size, ssize_t *result)
{
struct posix_acl *acl;
char *p = data + *result;
acl = get_inode_acl(inode, type);
if (IS_ERR_OR_NULL(acl))
return 0;
posix_acl_release(acl);
*result += strlen(name);
*result += 1;
if (!size)
return 0;
if (*result > size)
return -ERANGE;
strcpy(p, name);
return 0;
}
ssize_t
nfs3_listxattr(struct dentry *dentry, char *data, size_t size)
{
struct inode *inode = d_inode(dentry);
ssize_t result = 0;
int error;
error = nfs3_list_one_acl(inode, ACL_TYPE_ACCESS,
XATTR_NAME_POSIX_ACL_ACCESS, data, size, &result);
if (error)
return error;
error = nfs3_list_one_acl(inode, ACL_TYPE_DEFAULT,
XATTR_NAME_POSIX_ACL_DEFAULT, data, size, &result);
if (error)
return error;
return result;
}