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Message-ID: <20200804212214.GD1992048@gmail.com>
Date: Tue, 4 Aug 2020 14:22:14 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Daniel Colascione <dancol@...gle.com>
Cc: timmurray@...gle.com, selinux@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, viro@...iv.linux.org.uk, paul@...l-moore.com,
nnk@...gle.com, sds@...ho.nsa.gov, lokeshgidra@...gle.com,
jmorris@...ei.org
Subject: Re: [PATCH v5 1/3] Add a new LSM-supporting anonymous inode interface
On Wed, Apr 01, 2020 at 02:39:01PM -0700, 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@...gle.com>
> ---
> fs/anon_inodes.c | 191 ++++++++++++++++++++++++++++--------
> include/linux/anon_inodes.h | 13 +++
> include/linux/lsm_hooks.h | 11 +++
> include/linux/security.h | 3 +
> security/security.c | 9 ++
> 5 files changed, 186 insertions(+), 41 deletions(-)
>
> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 89714308c25b..f87f221167cf 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -55,61 +55,108 @@ 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)
> +{
> + 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 inode;
> + inode->i_flags &= ~S_PRIVATE;
> + error = security_inode_init_security_anon(
> + inode, &qname, context_inode);
> + if (error) {
> + iput(inode);
> + return ERR_PTR(error);
> + }
> + return inode;
> +}
> +
> +struct file *_anon_inode_getfile(const char *name,
> + const struct file_operations *fops,
> + void *priv, int flags,
> + const struct inode *context_inode,
> + bool secure)
Unnecessarily global function.
> {
> + struct inode *inode;
> struct file *file;
>
> - if (IS_ERR(anon_inode_inode))
> - return ERR_PTR(-ENODEV);
> + if (secure) {
> + inode = anon_inode_make_secure_inode(
> + name, context_inode);
> + if (IS_ERR(inode))
> + return ERR_PTR(PTR_ERR(inode));
Use ERR_CAST(), not ERR_PTR(PTR_ERR()).
> /**
> - * anon_inode_getfd - creates a new file instance by hooking it up to an
> - * anonymous inode, and a dentry that describe the "class"
> - * of the file
> + * anon_inode_getfile_secure - creates a new file instance by hooking
> + * it up to a new anonymous inode and a
> + * dentry that describe the "class" of the
> + * file. Make it possible to use security
> + * modules to control access to the
> + * new 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 an unspecified inode. This is
> + * useful for files that do not need to have a full-fledged filesystem
> + * to operate correctly. All the files created with
> + * anon_inode_getfile_secure() will have distinct inodes, avoiding
> + * code duplication for the file/inode/dentry setup. Returns the
> + * newly created file* or an error pointer.
> + */
> +struct file *anon_inode_getfile_secure(const char *name,
> + const struct file_operations *fops,
> + void *priv, int flags,
> + const struct inode *context_inode)
Why copy-and-paste this long comment if it's not even updated to document the
new argument?
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 20d8cf194fb7..5434c1d285b2 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -215,6 +215,13 @@
> * 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.
> + * @inode contains the inode structure
> + * @name name of the anonymous inode class
> + * @context_inode optional related inode
> + * Returns 0 on success. Returns -EPERM if the security module denies
> + * the creation of this inode.
Shouldn't it be EACCES?
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