[PATCH v2 3/9] mm/mshare: make msharefs writable and support directories

Khalid Aziz
2022-06-29T22:56:11Z

Make msharefs filesystem writable and allow creating directories
to support better access control to mshare'd regions defined in
msharefs.

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
---
mm/mshare.c | 195 +++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 186 insertions(+), 9 deletions(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index 3e448e11c742..2d5924d39221 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -21,11 +21,21 @@
#include <linux/fileattr.h>
#include <uapi/linux/magic.h>
#include <uapi/linux/limits.h>
+#include <uapi/linux/mman.h>

static struct super_block *msharefs_sb;

+static const struct inode_operations msharefs_dir_inode_ops;
+static const struct inode_operations msharefs_file_inode_ops;
+
+static int
+msharefs_open(struct inode *inode, struct file *file)
+{
+ return simple_open(inode, file);
+}
+
static const struct file_operations msharefs_file_operations = {
- .open = simple_open,
+ .open = msharefs_open,
.llseek = no_llseek,
};

@@ -42,6 +52,113 @@ msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr)
return 0;
}

+static struct dentry
+*msharefs_alloc_dentry(struct dentry *parent, const char *name)
+{
+ struct dentry *d;
+ struct qstr q;
+ int err;
+
+ q.name = name;
+ q.len = strlen(name);
+
+ err = msharefs_d_hash(parent, &q);
+ if (err)
+ return ERR_PTR(err);
+
+ d = d_alloc(parent, &q);
+ if (d)
+ return d;
+
+ return ERR_PTR(-ENOMEM);
+}
+
+static struct inode
+*msharefs_get_inode(struct super_block *sb, const struct inode *dir,
+ umode_t mode)
+{
+ struct inode *inode = new_inode(sb);
+
+ if (inode) {
+ inode->i_ino = get_next_ino();
+ inode_init_owner(&init_user_ns, inode, dir, mode);
+
+ inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
+
+ switch (mode & S_IFMT) {
+ case S_IFREG:
+ inode->i_op = &msharefs_file_inode_ops;
+ inode->i_fop = &msharefs_file_operations;
+ break;
+ case S_IFDIR:
+ inode->i_op = &msharefs_dir_inode_ops;
+ inode->i_fop = &simple_dir_operations;
+ inc_nlink(inode);
+ break;
+ case S_IFLNK:
+ inode->i_op = &page_symlink_inode_operations;
+ break;
+ default:
+ discard_new_inode(inode);
+ inode = NULL;
+ break;
+ }
+ }
+
+ return inode;
+}
+
+static int
+msharefs_mknod(struct user_namespace *mnt_userns, struct inode *dir,
+ struct dentry *dentry, umode_t mode, dev_t dev)
+{
+ struct inode *inode;
+ int err = 0;
+
+ inode = msharefs_get_inode(dir->i_sb, dir, mode);
+ if (IS_ERR(inode))
+ return PTR_ERR(inode);
+
+ d_instantiate(dentry, inode);
+ dget(dentry);
+ dir->i_mtime = dir->i_ctime = current_time(dir);
+
+ return err;
+}
+
+static int
+msharefs_create(struct user_namespace *mnt_userns, struct inode *dir,
+ struct dentry *dentry, umode_t mode, bool excl)
+{
+ return msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0);
+}
+
+static int
+msharefs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
+ struct dentry *dentry, umode_t mode)
+{
+ int ret = msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFDIR, 0);
+
+ if (!ret)
+ inc_nlink(dir);
+ return ret;
+}
+
+static const struct inode_operations msharefs_file_inode_ops = {
+ .setattr = simple_setattr,
+ .getattr = simple_getattr,
+};
+static const struct inode_operations msharefs_dir_inode_ops = {
+ .create = msharefs_create,
+ .lookup = simple_lookup,
+ .link = simple_link,
+ .unlink = simple_unlink,
+ .mkdir = msharefs_mkdir,
+ .rmdir = simple_rmdir,
+ .mknod = msharefs_mknod,
+ .rename = simple_rename,
+};
+
static void
mshare_evict_inode(struct inode *inode)
{
@@ -58,7 +175,7 @@ mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
{
char s[80];

- sprintf(s, "%ld", PGDIR_SIZE);
+ sprintf(s, "%ld\n", PGDIR_SIZE);
return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
}

@@ -72,6 +189,38 @@ static const struct super_operations mshare_s_ops = {
.evict_inode = mshare_evict_inode,
};

+static int
+prepopulate_files(struct super_block *s, struct inode *dir,
+ struct dentry *root, const struct tree_descr *files)
+{
+ int i;
+ struct inode *inode;
+ struct dentry *dentry;
+
+ for (i = 0; !files->name || files->name[0]; i++, files++) {
+ if (!files->name)
+ continue;
+
+ dentry = msharefs_alloc_dentry(root, files->name);
+ if (!dentry)
+ return -ENOMEM;
+
+ inode = msharefs_get_inode(s, dir, S_IFREG | files->mode);
+ if (!inode) {
+ dput(dentry);
+ return -ENOMEM;
+ }
+ inode->i_mode = S_IFREG | files->mode;
+ inode->i_atime = inode->i_mtime = inode->i_ctime
+ = current_time(inode);
+ inode->i_fop = files->ops;
+ inode->i_ino = i;
+ d_add(dentry, inode);
+ }
+
+ return 0;
+}
+
static int
msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
{
@@ -79,21 +228,49 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
[2] = { "mshare_info", &mshare_info_ops, 0444},
{""},
};
- int err;
+ struct inode *inode;
+ struct dentry *root;
+ int err = 0;

- err = simple_fill_super(sb, MSHARE_MAGIC, mshare_files);
- if (!err) {
- msharefs_sb = sb;
- sb->s_d_op = &msharefs_d_ops;
- sb->s_op = &mshare_s_ops;
+ sb->s_blocksize = PAGE_SIZE;
+ sb->s_blocksize_bits = PAGE_SHIFT;
+ sb->s_magic = MSHARE_MAGIC;
+ sb->s_op = &mshare_s_ops;
+ sb->s_d_op = &msharefs_d_ops;
+ sb->s_time_gran = 1;
+
+ inode = msharefs_get_inode(sb, NULL, S_IFDIR | 0777);
+ if (!inode) {
+ err = -ENOMEM;
+ goto out;
}
+ inode->i_ino = 1;
+ root = d_make_root(inode);
+ if (!root) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ err = prepopulate_files(sb, inode, root, mshare_files);
+ if (err < 0)
+ goto clean_root;
+
+ sb->s_root = root;
+ msharefs_sb = sb;
+ return err;
+
+clean_root:
+ d_genocide(root);
+ shrink_dcache_parent(root);
+ dput(root);
+out:
return err;
}

static int
msharefs_get_tree(struct fs_context *fc)
{
- return get_tree_single(fc, msharefs_fill_super);
+ return get_tree_nodev(fc, msharefs_fill_super);
}

static const struct fs_context_operations msharefs_context_ops = {
--
2.32.0