[v3,2/3] Teach SELinux about anonymous inodes
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Message ID 20200326181456.132742-3-dancol@google.com
State New
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Series
  • [v3,1/3] Add a new LSM-supporting anonymous inode interface
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Commit Message

Daniel Colascione March 26, 2020, 6:14 p.m. UTC
This change uses the anon_inodes and LSM infrastructure introduced in
the previous patch to give SELinux the ability to control
anonymous-inode files that are created using the new _secure()
anon_inodes functions.

A SELinux policy author detects and controls these anonymous inodes by
adding a name-based type_transition rule that assigns a new security
type to anonymous-inode files created in some domain. The name used
for the name-based transition is the name associated with the
anonymous inode for file listings --- e.g., "[userfaultfd]" or
"[perf_event]".

Example:

type uffd_t;
type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]";
allow sysadm_t uffd_t:anon_inode { create };

(The next patch in this series is necessary for making userfaultfd
support this new interface.  The example above is just
for exposition.)

Signed-off-by: Daniel Colascione <dancol@google.com>
---
 security/selinux/hooks.c            | 54 +++++++++++++++++++++++++++++
 security/selinux/include/classmap.h |  2 ++
 2 files changed, 56 insertions(+)

Comments

Stephen Smalley March 26, 2020, 7:02 p.m. UTC | #1
On 3/26/20 2:14 PM, Daniel Colascione wrote:
> This change uses the anon_inodes and LSM infrastructure introduced in
> the previous patch to give SELinux the ability to control
> anonymous-inode files that are created using the new _secure()
> anon_inodes functions.
> 
> A SELinux policy author detects and controls these anonymous inodes by
> adding a name-based type_transition rule that assigns a new security
> type to anonymous-inode files created in some domain. The name used
> for the name-based transition is the name associated with the
> anonymous inode for file listings --- e.g., "[userfaultfd]" or
> "[perf_event]".
> 
> Example:
> 
> type uffd_t;
> type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]";
> allow sysadm_t uffd_t:anon_inode { create };
> 
> (The next patch in this series is necessary for making userfaultfd
> support this new interface.  The example above is just
> for exposition.)
> 
> Signed-off-by: Daniel Colascione <dancol@google.com>
> ---
>   security/selinux/hooks.c            | 54 +++++++++++++++++++++++++++++
>   security/selinux/include/classmap.h |  2 ++
>   2 files changed, 56 insertions(+)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 1659b59fb5d7..b9eb45c2e4e5 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2915,6 +2915,59 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
>   	return 0;
>   }
>   
> +static int selinux_inode_init_security_anon(struct inode *inode,
> +					    const struct qstr *name,
> +					    const struct file_operations *fops,
> +					    const struct inode *context_inode)
> +{
> +	const struct task_security_struct *tsec = selinux_cred(current_cred());
> +	struct common_audit_data ad;
> +	struct inode_security_struct *isec;
> +	int rc;
> +
> +	if (unlikely(!selinux_state.initialized))
> +		return 0;
> +
> +	isec = selinux_inode(inode);
> +
> +	/*
> +	 * We only get here once per ephemeral inode.  The inode has
> +	 * been initialized via inode_alloc_security but is otherwise
> +	 * untouched.
> +	 */
> +
> +	if (context_inode) {
> +		struct inode_security_struct *context_isec =
> +			selinux_inode(context_inode);
> +		isec->sclass = context_isec->sclass;
> +		isec->sid = context_isec->sid;
> +	} else {
> +		isec->sclass = SECCLASS_ANON_INODE;
> +		rc = security_transition_sid(
> +			&selinux_state, tsec->sid, tsec->sid,
> +			SECCLASS_FILE, name, &isec->sid);

I guess you missed the 2nd comment in my reply to v2 of this patch:
You should use isec->sclass aka SECCLASS_ANON_INODE instead of 
SECCLASS_FILE here.

Patch
diff mbox series

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1659b59fb5d7..b9eb45c2e4e5 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2915,6 +2915,59 @@  static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	return 0;
 }
 
+static int selinux_inode_init_security_anon(struct inode *inode,
+					    const struct qstr *name,
+					    const struct file_operations *fops,
+					    const struct inode *context_inode)
+{
+	const struct task_security_struct *tsec = selinux_cred(current_cred());
+	struct common_audit_data ad;
+	struct inode_security_struct *isec;
+	int rc;
+
+	if (unlikely(!selinux_state.initialized))
+		return 0;
+
+	isec = selinux_inode(inode);
+
+	/*
+	 * We only get here once per ephemeral inode.  The inode has
+	 * been initialized via inode_alloc_security but is otherwise
+	 * untouched.
+	 */
+
+	if (context_inode) {
+		struct inode_security_struct *context_isec =
+			selinux_inode(context_inode);
+		isec->sclass = context_isec->sclass;
+		isec->sid = context_isec->sid;
+	} else {
+		isec->sclass = SECCLASS_ANON_INODE;
+		rc = security_transition_sid(
+			&selinux_state, tsec->sid, tsec->sid,
+			SECCLASS_FILE, name, &isec->sid);
+		if (rc)
+			return rc;
+	}
+
+	isec->initialized = LABEL_INITIALIZED;
+
+	/*
+	 * Now that we've initialized security, check whether we're
+	 * allowed to actually create this type of anonymous inode.
+	 */
+
+	ad.type = LSM_AUDIT_DATA_INODE;
+	ad.u.inode = inode;
+
+	return avc_has_perm(&selinux_state,
+			    tsec->sid,
+			    isec->sid,
+			    isec->sclass,
+			    FILE__CREATE,
+			    &ad);
+}
+
 static int selinux_inode_create(struct inode *dir, struct dentry *dentry, umode_t mode)
 {
 	return may_create(dir, dentry, SECCLASS_FILE);
@@ -6923,6 +6976,7 @@  static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 
 	LSM_HOOK_INIT(inode_free_security, selinux_inode_free_security),
 	LSM_HOOK_INIT(inode_init_security, selinux_inode_init_security),
+	LSM_HOOK_INIT(inode_init_security_anon, selinux_inode_init_security_anon),
 	LSM_HOOK_INIT(inode_create, selinux_inode_create),
 	LSM_HOOK_INIT(inode_link, selinux_inode_link),
 	LSM_HOOK_INIT(inode_unlink, selinux_inode_unlink),
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 986f3ac14282..263750b6aaac 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -248,6 +248,8 @@  struct security_class_mapping secclass_map[] = {
 	  {"open", "cpu", "kernel", "tracepoint", "read", "write"} },
 	{ "lockdown",
 	  { "integrity", "confidentiality", NULL } },
+	{ "anon_inode",
+	  { COMMON_FILE_PERMS, NULL } },
 	{ NULL }
   };