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Message-ID: <CAGXu5jKzruTtA8-cQALViKfL=txR=zKTO7jFhf9CTxWxHLjckQ@mail.gmail.com>
Date: Wed, 24 May 2017 12:27:49 -0700
From: Kees Cook <keescook@...gle.com>
To: John Johansen <john.johansen@...onical.com>
Cc: linux-security-module <linux-security-module@...r.kernel.org>,
James Morris <jmorris@...ei.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] securityfs: add the ability to support symlinks
On Wed, May 10, 2017 at 7:46 PM, John Johansen
<john.johansen@...onical.com> wrote:
> Signed-off-by: John Johansen <john.johansen@...onical.com>
> Reviewed-by: Seth Arnold <seth.arnold@...onical.com>
This looks correct to me; it matches what other pseudo-filesystems do,
and provides the expected interfaces.
Acked-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> include/linux/security.h | 12 ++++
> security/inode.c | 140 +++++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 134 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 78d8e03be5d3..28e2be5dd6df 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -1645,6 +1645,10 @@ extern struct dentry *securityfs_create_file(const char *name, umode_t mode,
> struct dentry *parent, void *data,
> const struct file_operations *fops);
> extern struct dentry *securityfs_create_dir(const char *name, struct dentry *parent);
> +struct dentry *securityfs_create_symlink(const char *name,
> + struct dentry *parent,
> + const char *target,
> + const struct inode_operations *iops);
> extern void securityfs_remove(struct dentry *dentry);
>
> #else /* CONFIG_SECURITYFS */
> @@ -1664,6 +1668,14 @@ static inline struct dentry *securityfs_create_file(const char *name,
> return ERR_PTR(-ENODEV);
> }
>
> +struct dentry *securityfs_create_symlink(const char *name,
> + struct dentry *parent,
> + const char *target,
> + const struct inode_operations *iops)
> +{
> + return ERR_PTR(-ENODEV);
> +}
> +
> static inline void securityfs_remove(struct dentry *dentry)
> {}
>
> diff --git a/security/inode.c b/security/inode.c
> index 2cb14162ff8d..10c4955d0bed 100644
> --- a/security/inode.c
> +++ b/security/inode.c
> @@ -26,11 +26,31 @@
> static struct vfsmount *mount;
> static int mount_count;
>
> +static void securityfs_evict_inode(struct inode *inode)
> +{
> + truncate_inode_pages_final(&inode->i_data);
> + clear_inode(inode);
> + if (S_ISLNK(inode->i_mode))
> + kfree(inode->i_link);
> +}
> +
> +static const struct super_operations securityfs_super_operations = {
> + .statfs = simple_statfs,
> + .evict_inode = securityfs_evict_inode,
> +};
> +
> static int fill_super(struct super_block *sb, void *data, int silent)
> {
> static struct tree_descr files[] = {{""}};
> + int error;
> +
> + error = simple_fill_super(sb, SECURITYFS_MAGIC, files);
> + if (error)
> + return error;
> +
> + sb->s_op = &securityfs_super_operations;
>
> - return simple_fill_super(sb, SECURITYFS_MAGIC, files);
> + return 0;
> }
>
> static struct dentry *get_sb(struct file_system_type *fs_type,
> @@ -48,7 +68,7 @@ static struct file_system_type fs_type = {
> };
>
> /**
> - * securityfs_create_file - create a file in the securityfs filesystem
> + * securityfs_create_dentry - create a dentry in the securityfs filesystem
> *
> * @name: a pointer to a string containing the name of the file to create.
> * @mode: the permission that the file should have
> @@ -60,34 +80,35 @@ static struct file_system_type fs_type = {
> * the open() call.
> * @fops: a pointer to a struct file_operations that should be used for
> * this file.
> + * @iops: a point to a struct of inode_operations that should be used for
> + * this file/dir
> *
> - * This is the basic "create a file" function for securityfs. It allows for a
> - * wide range of flexibility in creating a file, or a directory (if you
> - * want to create a directory, the securityfs_create_dir() function is
> - * recommended to be used instead).
> + * This is the basic "create a file/dir/symlink" function for
> + * securityfs. It allows for a wide range of flexibility in creating
> + * a file, or a directory (if you want to create a directory, the
> + * securityfs_create_dir() function is recommended to be used
> + * instead).
> *
> * This function returns a pointer to a dentry if it succeeds. This
> - * pointer must be passed to the securityfs_remove() function when the file is
> - * to be removed (no automatic cleanup happens if your module is unloaded,
> - * you are responsible here). If an error occurs, the function will return
> - * the error value (via ERR_PTR).
> + * pointer must be passed to the securityfs_remove() function when the
> + * file is to be removed (no automatic cleanup happens if your module
> + * is unloaded, you are responsible here). If an error occurs, the
> + * function will return the error value (via ERR_PTR).
> *
> * If securityfs is not enabled in the kernel, the value %-ENODEV is
> * returned.
> */
> -struct dentry *securityfs_create_file(const char *name, umode_t mode,
> - struct dentry *parent, void *data,
> - const struct file_operations *fops)
> +static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
> + struct dentry *parent, void *data,
> + const struct file_operations *fops,
> + const struct inode_operations *iops)
> {
> struct dentry *dentry;
> - int is_dir = S_ISDIR(mode);
> struct inode *dir, *inode;
> int error;
>
> - if (!is_dir) {
> - BUG_ON(!fops);
> + if (!(mode & S_IFMT))
> mode = (mode & S_IALLUGO) | S_IFREG;
> - }
>
> pr_debug("securityfs: creating file '%s'\n",name);
>
> @@ -120,11 +141,14 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
> inode->i_mode = mode;
> inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
> inode->i_private = data;
> - if (is_dir) {
> + if (S_ISDIR(mode)) {
> inode->i_op = &simple_dir_inode_operations;
> inode->i_fop = &simple_dir_operations;
> inc_nlink(inode);
> inc_nlink(dir);
> + } else if (S_ISLNK(mode)) {
> + inode->i_op = iops ? iops : &simple_symlink_inode_operations;
> + inode->i_link = data;
> } else {
> inode->i_fop = fops;
> }
> @@ -141,6 +165,38 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
> simple_release_fs(&mount, &mount_count);
> return dentry;
> }
> +
> +/**
> + * securityfs_create_file - create a file in the securityfs filesystem
> + *
> + * @name: a pointer to a string containing the name of the file to create.
> + * @mode: the permission that the file should have
> + * @parent: a pointer to the parent dentry for this file. This should be a
> + * directory dentry if set. If this parameter is %NULL, then the
> + * file will be created in the root of the securityfs filesystem.
> + * @data: a pointer to something that the caller will want to get to later
> + * on. The inode.i_private pointer will point to this value on
> + * the open() call.
> + * @fops: a pointer to a struct file_operations that should be used for
> + * this file.
> + *
> + * This function creates a file in securityfs with the given @name.
> + *
> + * This function returns a pointer to a dentry if it succeeds. This
> + * pointer must be passed to the securityfs_remove() function when the file is
> + * to be removed (no automatic cleanup happens if your module is unloaded,
> + * you are responsible here). If an error occurs, the function will return
> + * the error value (via ERR_PTR).
> + *
> + * If securityfs is not enabled in the kernel, the value %-ENODEV is
> + * returned.
> + */
> +struct dentry *securityfs_create_file(const char *name, umode_t mode,
> + struct dentry *parent, void *data,
> + const struct file_operations *fops)
> +{
> + return securityfs_create_dentry(name, mode, parent, data, fops, NULL);
> +}
> EXPORT_SYMBOL_GPL(securityfs_create_file);
>
> /**
> @@ -172,6 +228,54 @@ struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
> EXPORT_SYMBOL_GPL(securityfs_create_dir);
>
> /**
> + * securityfs_create_symlink - create a symlink in the securityfs filesystem
> + *
> + * @name: a pointer to a string containing the name of the symlink to
> + * create.
> + * @parent: a pointer to the parent dentry for the symlink. This should be a
> + * directory dentry if set. If this parameter is %NULL, then the
> + * directory will be created in the root of the securityfs filesystem.
> + * @target: a pointer to a string containing the name of the symlink's target.
> + * If this parameter is %NULL, then the @iops parameter needs to be
> + * setup to handle .readlink and .get_link inode_operations.
> + * @iops: a pointer to the struct inode_operations to use for the symlink. If
> + * this parameter is %NULL, then the default simple_symlink_inode
> + * operations will be used.
> + *
> + * This function creates a symlink in securityfs with the given @name.
> + *
> + * This function returns a pointer to a dentry if it succeeds. This
> + * pointer must be passed to the securityfs_remove() function when the file is
> + * to be removed (no automatic cleanup happens if your module is unloaded,
> + * you are responsible here). If an error occurs, the function will return
> + * the error value (via ERR_PTR).
> + *
> + * If securityfs is not enabled in the kernel, the value %-ENODEV is
> + * returned.
> + */
> +struct dentry *securityfs_create_symlink(const char *name,
> + struct dentry *parent,
> + const char *target,
> + const struct inode_operations *iops)
> +{
> + struct dentry *dent;
> + char *link = NULL;
> +
> + if (target) {
> + link = kstrdup(target, GFP_KERNEL);
> + if (!link)
> + return ERR_PTR(-ENOMEM);
> + }
> + dent = securityfs_create_dentry(name, S_IFLNK | S_IRUGO, parent,
> + link, NULL, iops);
> + if (IS_ERR(dent))
> + kfree(link);
> +
> + return dent;
> +}
> +EXPORT_SYMBOL_GPL(securityfs_create_symlink);
> +
> +/**
> * securityfs_remove - removes a file or directory from the securityfs filesystem
> *
> * @dentry: a pointer to a the dentry of the file or directory to be removed.
> --
> 2.11.0
>
--
Kees Cook
Pixel Security
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