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SubjectRe: [PATCH v2 1/3] Add a new LSM-supporting anonymous inode interface
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On 3/25/20 7:02 PM, Daniel Colascione wrote:
> This change adds two new functions, anon_inode_getfile_secure and
> anon_inode_getfd_secure, that create anonymous-node files with
> individual non-S_PRIVATE inodes to which security modules can apply
> policy. Existing callers continue using the original singleton-inode
> kind of anonymous-inode file. We can transition anonymous inode users
> to the new kind of anonymous inode in individual patches for the sake
> of bisection and review.
>
> The new functions accept an optional context_inode parameter that
> callers can use to provide additional contextual information to
> security modules, e.g., indicating that one anonymous struct file is a
> logical child of another, allowing a security model to propagate
> security information from one to the other.
>
> Signed-off-by: Daniel Colascione <dancol@google.com>
> ---

> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 89714308c25b..114a04fc1db4 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -55,75 +55,135 @@ static struct file_system_type anon_inode_fs_type = {
> .kill_sb = kill_anon_super,
> };
>
> -/**
> - * anon_inode_getfile - creates a new file instance by hooking it up to an
> - * anonymous inode, and a dentry that describe the "class"
> - * of the file
> - *
> - * @name: [in] name of the "class" of the new file
> - * @fops: [in] file operations for the new file
> - * @priv: [in] private data for the new file (will be file's private_data)
> - * @flags: [in] flags
> - *
> - * Creates a new file by hooking it on a single inode. This is useful for files
> - * that do not need to have a full-fledged inode in order to operate correctly.
> - * All the files created with anon_inode_getfile() will share a single inode,
> - * hence saving memory and avoiding code duplication for the file/inode/dentry
> - * setup. Returns the newly created file* or an error pointer.
> - */
> -struct file *anon_inode_getfile(const char *name,
> - const struct file_operations *fops,
> - void *priv, int flags)
> +static struct inode *anon_inode_make_secure_inode(
> + const char *name,
> + const struct inode *context_inode,
> + const struct file_operations *fops)
> +{
> + struct inode *inode;
> + const struct qstr qname = QSTR_INIT(name, strlen(name));
> + int error;
> +
> + inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
> + if (IS_ERR(inode))
> + return ERR_PTR(PTR_ERR(inode));

Just return inode here?

> + inode->i_flags &= ~S_PRIVATE;
> + error = security_inode_init_security_anon(
> + inode, &qname, fops, context_inode);

Would drop fops argument to the security hook until we have an actual
user of it; one can always add it later.


> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 37df7c9eedb1..07b0f6e03849 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1014,8 +1014,6 @@ static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
> }
> }
>
> -static const struct file_operations userfaultfd_fops;
> -
> static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
> struct userfaultfd_ctx *new,
> struct uffd_msg *msg)
> @@ -1920,7 +1918,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
> }
> #endif
>
> -static const struct file_operations userfaultfd_fops = {
> +const struct file_operations userfaultfd_fops = {
> #ifdef CONFIG_PROC_FS
> .show_fdinfo = userfaultfd_show_fdinfo,
> #endif

These changes can be dropped entirely AFAICT.

> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 20d8cf194fb7..de5d37e388df 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -215,6 +215,10 @@
> * Returns 0 if @name and @value have been successfully set,
> * -EOPNOTSUPP if no security attribute is needed, or
> * -ENOMEM on memory allocation failure.
> + * @inode_init_security_anon:
> + * Set up a secure anonymous inode.
> + * Returns 0 on success. Returns -EPERM if the security module denies
> + * the creation of this inode.

I'd favor describing the arguments (@name, @context_inode) too.

> * @inode_create:
> * Check permission to create a regular file.
> * @dir contains inode structure of the parent of the new file.
> @@ -1552,6 +1556,10 @@ union security_list_options {
> const struct qstr *qstr,
> const char **name, void **value,
> size_t *len);
> + int (*inode_init_security_anon)(struct inode *inode,
> + const struct qstr *name,
> + const struct file_operations *fops,
> + const struct inode *context_inode);
> int (*inode_create)(struct inode *dir, struct dentry *dentry,

Can drop the fops argument.

> diff --git a/include/linux/security.h b/include/linux/security.h
> index 64b19f050343..8ea76af0be7a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -320,6 +320,10 @@ void security_inode_free(struct inode *inode);
> int security_inode_init_security(struct inode *inode, struct inode *dir,
> const struct qstr *qstr,
> initxattrs initxattrs, void *fs_data);
> +int security_inode_init_security_anon(struct inode *inode,
> + const struct qstr *name,
> + const struct file_operations *fops,
> + const struct inode *context_inode);

Ditto

> diff --git a/security/security.c b/security/security.c
> index 565bc9b67276..d06f3969c030 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1033,6 +1033,16 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
> }
> EXPORT_SYMBOL(security_inode_init_security);
>
> +int
> +security_inode_init_security_anon(struct inode *inode,
> + const struct qstr *name,
> + const struct file_operations *fops,
> + const struct inode *context_inode)
> +{
> + return call_int_hook(inode_init_security_anon, 0, inode, name,
> + fops, context_inode);
> +}
> +

And again.


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