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Message-ID: <CA+EESO7YG=9K7o=rjRm++n7HWPhhP1W8Xo7CF_4_pGBheExmqA@mail.gmail.com>
Date: Tue, 25 Aug 2020 17:25:35 -0700
From: Lokesh Gidra <lokeshgidra@...gle.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
James Morris <jmorris@...ei.org>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Casey Schaufler <casey@...aufler-ca.com>,
"Serge E. Hallyn" <serge@...lyn.com>,
Paul Moore <paul@...l-moore.com>,
Eric Paris <eparis@...isplace.org>,
Daniel Colascione <dancol@...col.org>,
Kees Cook <keescook@...omium.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
KP Singh <kpsingh@...gle.com>,
David Howells <dhowells@...hat.com>,
Thomas Cedeno <thomascedeno@...gle.com>,
Anders Roxell <anders.roxell@...aro.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
Matthew Garrett <matthewgarrett@...gle.com>,
Aaron Goidel <acgoide@...ho.nsa.gov>,
Randy Dunlap <rdunlap@...radead.org>,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
YueHaibing <yuehaibing@...wei.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Alexei Starovoitov <ast@...nel.org>,
Alexey Budankov <alexey.budankov@...ux.intel.com>,
Adrian Reber <areber@...hat.com>,
Aleksa Sarai <cyphar@...har.com>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
LSM List <linux-security-module@...r.kernel.org>,
SElinux list <selinux@...r.kernel.org>,
Kalesh Singh <kaleshsingh@...gle.com>,
Calin Juravle <calin@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Nick Kralevich <nnk@...gle.com>,
Jeffrey Vander Stoep <jeffv@...gle.com>,
kernel-team@...roid.com, Daniel Colascione <dancol@...gle.com>
Subject: Re: [PATCH v7 1/3] Add a new LSM-supporting anonymous inode interface
On Mon, Aug 24, 2020 at 8:50 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Fri, Aug 21, 2020 at 11:56:43AM -0700, Lokesh Gidra wrote:
> > From: Daniel Colascione <dancol@...gle.com>
> >
> > This change adds a new function, anon_inode_getfd_secure, that creates
> > anonymous-node file with individual non-S_PRIVATE inode 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 function accepts an optional context_inode parameter that
> > callers can use to provide additional contextual information to
> > security modules for granting/denying permission to create an anon inode
> > of the same type.
> >
> > For example, in case of userfaultfd, the created inode is a
> > 'logical child' of the context_inode (userfaultfd inode of the
> > parent process) in the sense that it provides the security context
> > required during creation of the child process' userfaultfd inode.
> >
> > Signed-off-by: Daniel Colascione <dancol@...gle.com>
> >
> > [Fix comment documenting return values of inode_init_security_anon()]
> > [Add context_inode description in comments to anon_inode_getfd_secure()]
> > [Remove definition of anon_inode_getfile_secure() as there are no callers]
> > [Make _anon_inode_getfile() static]
> > [Use correct error cast in _anon_inode_getfile()]
> >
> > Signed-off-by: Lokesh Gidra <lokeshgidra@...gle.com>
> > ---
> > fs/anon_inodes.c | 148 ++++++++++++++++++++++++----------
> > include/linux/anon_inodes.h | 13 +++
> > include/linux/lsm_hook_defs.h | 2 +
> > include/linux/lsm_hooks.h | 7 ++
> > include/linux/security.h | 3 +
> > security/security.c | 9 +++
> > 6 files changed, 141 insertions(+), 41 deletions(-)
> >
> > diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> > index 89714308c25b..2aa8b57be895 100644
> > --- a/fs/anon_inodes.c
> > +++ b/fs/anon_inodes.c
> > @@ -55,61 +55,78 @@ 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);
>
> Weird indentation here. The call to security_inode_init_security_anon() fits on
> one line.
>
> > + if (error) {
> > + iput(inode);
> > + return ERR_PTR(error);
> > + }
> > + return inode;
> > +}
> > +
> > +static struct file *_anon_inode_getfile(const char *name,
> > + const struct file_operations *fops,
> > + void *priv, int flags,
> > + const struct inode *context_inode,
> > + bool secure)
> > {
> > + 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);
>
> Likewise here. The call to anon_inode_make_secure_inode() fits on one line.
>
> > + if (IS_ERR(inode))
> > + return ERR_CAST(inode);
> > + } else {
> > + inode = anon_inode_inode;
> > + if (IS_ERR(inode))
> > + return ERR_PTR(-ENODEV);
> > + /*
> > + * We know the anon_inode inode count is always
> > + * greater than zero, so ihold() is safe.
> > + */
> > + ihold(inode);
> > + }
> >
> > - if (fops->owner && !try_module_get(fops->owner))
> > - return ERR_PTR(-ENOENT);
> > + if (fops->owner && !try_module_get(fops->owner)) {
> > + file = ERR_PTR(-ENOENT);
> > + goto err;
> > + }
>
> The error path here does module_put(fops->owner), even though a reference wasn't
> acquired.
>
> > +
> > +/**
> > + * 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
> > + *
> > + * @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 use the same singleton inode, reducing
>
> This should say anon_inode_getfd(), not anon_inode_getfile().
>
> > +/**
> > + * Like anon_inode_getfd(), but adds the @context_inode argument to
> > + * allow security modules to control creation of the new file. Once the
> > + * security module makes the decision, this inode is no longer needed
> > + * and hence reference to it is not held.
> > + */
> > +int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
> > + void *priv, int flags,
> > + const struct inode *context_inode)
> > +{
> > + return _anon_inode_getfd(name, fops, priv, flags,
> > + context_inode, true);
> > +}
>
> Weird indentation here again. The call to _anon_inode_getfd() fits on one line.
>
> > @@ -162,4 +229,3 @@ static int __init anon_inode_init(void)
> > }
> >
> > fs_initcall(anon_inode_init);
> > -
>
> Unnecessary whitespace change.
>
> > diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
> > index d0d7d96261ad..67bd85d92dca 100644
> > --- a/include/linux/anon_inodes.h
> > +++ b/include/linux/anon_inodes.h
> > @@ -10,12 +10,25 @@
> > #define _LINUX_ANON_INODES_H
> >
> > struct file_operations;
> > +struct inode;
> > +
> > +struct file *anon_inode_getfile_secure(const char *name,
> > + const struct file_operations *fops,
> > + void *priv, int flags,
> > + const struct inode *context_inode);
>
> This function isn't defined anywhere.
>
> > + * @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, -EACCESS if the security module denies the
> > + * creation of this inode, or another -errno upon other errors.
>
> Is there a better name for this than "secure anonymous inode"?
> (What is meant by "secure"?)
>
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index 0a0a03b36a3b..95c133a8f8bb 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -322,6 +322,9 @@ 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 inode *context_inode);
> > int security_old_inode_init_security(struct inode *inode, struct inode *dir,
> > const struct qstr *qstr, const char **name,
> > void **value, size_t *len);
>
> This patch doesn't compile when !CONFIG_SECURITY because this file is missing a
> !CONFIG_SECURITY stub for security_inode_init_security_anon().
>
> > diff --git a/security/security.c b/security/security.c
> > index 70a7ad357bc6..149b3f024e2d 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -1057,6 +1057,15 @@ 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 inode *context_inode)
> > +{
> > + return call_int_hook(inode_init_security_anon, 0, inode, name,
> > + context_inode);
> > +}
>
> Nit: everything else in this file has 'int' on the same line as the function
> name.
>
Thanks a lot for reviewing. I'll send another version with all these fixed.
> - Eric
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