Message-ID: <20110617171152.GA1389@albatros>
Date:	Fri, 17 Jun 2011 21:11:54 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, apparmor@...ts.ubuntu.com,
	"selinux@...ho.nsa.gov Stephen Smalley" <sds@...ho.nsa.gov>,
	James Morris <jmorris@...ei.org>,
	Eric Paris <eparis@...isplace.org>,
	John Johansen <john.johansen@...onical.com>,
	kernel-hardening@...ts.openwall.com
Subject: [RFC v2] security: intoduce ptrace_task_may_access_current

This patch adds ptrace_task_may_access_current() function.  It behaves
like ptrace_may_access(), but checks whether a specific task may ptrace
current.  The patch adds some new *capable*() functions with additional
task argument (instead of default current task_struct).  It also changes
security_ops->ptrace_access_check() by adding new argument and fixing
related LSM handlers in SELinux, AppArmor and SMACK.

v2 - renamed ptrace_access_check() back, added missing functions in
     headers, introduced actual ptrace_task_may_access_current().

Signed-off-by: Vasiliy Kulikov <segoon@...nwall.com>
---
 include/linux/capability.h    |    2 ++
 include/linux/ptrace.h        |    3 ++-
 include/linux/security.h      |   31 +++++++++++++++++++++++++++----
 kernel/capability.c           |   35 +++++++++++++++++++++++++----------
 kernel/ptrace.c               |   30 +++++++++++++++++++++++-------
 security/apparmor/lsm.c       |    8 ++++----
 security/commoncap.c          |    7 ++++---
 security/security.c           |   17 ++++++++++++++---
 security/selinux/hooks.c      |   11 +++++------
 security/smack/smack.h        |    1 +
 security/smack/smack_access.c |   25 +++++++++++++++++++++----
 security/smack/smack_lsm.c    |    7 ++++---
 12 files changed, 132 insertions(+), 45 deletions(-)

---
diff --git a/include/linux/capability.h b/include/linux/capability.h
index c421123..cc0bcfe 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -544,7 +544,9 @@ extern bool has_ns_capability(struct task_struct *t,
 			      struct user_namespace *ns, int cap);
 extern bool has_capability_noaudit(struct task_struct *t, int cap);
 extern bool capable(int cap);
+extern bool task_capable(struct task_struct *task, int cap);
 extern bool ns_capable(struct user_namespace *ns, int cap);
+extern bool ns_task_capable(struct task_struct *t, struct user_namespace *ns, int cap);
 extern bool task_ns_capable(struct task_struct *t, int cap);
 extern bool nsown_capable(int cap);
 
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 9178d5c..bb59e43 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -116,9 +116,10 @@ extern void exit_ptrace(struct task_struct *tracer);
 #define PTRACE_MODE_READ   1
 #define PTRACE_MODE_ATTACH 2
 /* Returns 0 on success, -errno on denial. */
-extern int __ptrace_may_access(struct task_struct *task, unsigned int mode);
+extern int __ptrace_may_access(struct task_struct *who, struct task_struct *task, unsigned int mode);
 /* Returns true on success, false on denial. */
 extern bool ptrace_may_access(struct task_struct *task, unsigned int mode);
+extern bool ptrace_task_may_access_current(struct task_struct *task, unsigned int mode);
 
 static inline int ptrace_reparented(struct task_struct *child)
 {
diff --git a/include/linux/security.h b/include/linux/security.h
index 8ce59ef..fb79dd5 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -56,7 +56,8 @@ struct user_namespace;
 extern int cap_capable(struct task_struct *tsk, const struct cred *cred,
 		       struct user_namespace *ns, int cap, int audit);
 extern int cap_settime(const struct timespec *ts, const struct timezone *tz);
-extern int cap_ptrace_access_check(struct task_struct *child, unsigned int mode);
+extern int cap_ptrace_access_check(struct task_struct *task, struct task_struct *child,
+	unsigned int mode);
 extern int cap_ptrace_traceme(struct task_struct *parent);
 extern int cap_capget(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted);
 extern int cap_capset(struct cred *new, const struct cred *old,
@@ -1375,7 +1376,9 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
 struct security_operations {
 	char name[SECURITY_NAME_MAX + 1];
 
-	int (*ptrace_access_check) (struct task_struct *child, unsigned int mode);
+	int (*ptrace_access_check) (struct task_struct *task,
+					 struct task_struct *child,
+					 unsigned int mode);
 	int (*ptrace_traceme) (struct task_struct *parent);
 	int (*capget) (struct task_struct *target,
 		       kernel_cap_t *effective,
@@ -1657,6 +1660,8 @@ extern int security_module_enable(struct security_operations *ops);
 extern int register_security(struct security_operations *ops);
 
 /* Security operations */
+int security_ptrace_task_access_check(struct task_struct *task,
+		 struct task_struct *child, unsigned int mode);
 int security_ptrace_access_check(struct task_struct *child, unsigned int mode);
 int security_ptrace_traceme(struct task_struct *parent);
 int security_capget(struct task_struct *target,
@@ -1667,6 +1672,10 @@ int security_capset(struct cred *new, const struct cred *old,
 		    const kernel_cap_t *effective,
 		    const kernel_cap_t *inheritable,
 		    const kernel_cap_t *permitted);
+int security_task_capable(struct task_struct *task,
+			struct user_namespace *ns,
+			const struct cred *cred,
+			int cap);
 int security_capable(struct user_namespace *ns, const struct cred *cred,
 			int cap);
 int security_real_capable(struct task_struct *tsk, struct user_namespace *ns,
@@ -1837,10 +1846,16 @@ static inline int security_init(void)
 	return 0;
 }
 
+static inline int security_ptrace_task_access_check(struct task_struct *task,
+		 struct task_struct *child, unsigned int mode)
+{
+	return cap_ptrace_access_check(task, child, mode);
+}
+
 static inline int security_ptrace_access_check(struct task_struct *child,
 					     unsigned int mode)
 {
-	return cap_ptrace_access_check(child, mode);
+	return cap_ptrace_access_check(current, child, mode);
 }
 
 static inline int security_ptrace_traceme(struct task_struct *parent)
@@ -1865,10 +1880,18 @@ static inline int security_capset(struct cred *new,
 	return cap_capset(new, old, effective, inheritable, permitted);
 }
 
+static inline int security_task_capable(struct task_struct *task,
+					struct user_namespace *ns,
+					const struct cred *cred,
+					int cap)
+{
+	return cap_capable(task, cred, ns, cap, SECURITY_CAP_AUDIT);
+}
+
 static inline int security_capable(struct user_namespace *ns,
 				   const struct cred *cred, int cap)
 {
-	return cap_capable(current, cred, ns, cap, SECURITY_CAP_AUDIT);
+	return security_task_capable(current, ns, cred, cap);
 }
 
 static inline int security_real_capable(struct task_struct *tsk, struct user_namespace *ns, int cap)
diff --git a/kernel/capability.c b/kernel/capability.c
index 283c529..bc9b07f 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -356,6 +356,30 @@ bool capable(int cap)
 }
 EXPORT_SYMBOL(capable);
 
+bool task_capable(struct task_struct *task, int cap)
+{
+	return ns_task_capable(task, &init_user_ns, cap);
+}
+EXPORT_SYMBOL(task_capable);
+
+bool ns_task_capable(struct task_struct *task, struct user_namespace *ns, int cap)
+{
+	if (unlikely(!cap_valid(cap))) {
+		printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
+		BUG();
+	}
+
+	rcu_read_lock();
+	if (security_task_capable(task, ns, __task_cred(task), cap) == 0) {
+		rcu_read_unlock();
+		current->flags |= PF_SUPERPRIV;
+		return true;
+	}
+	rcu_read_unlock();
+	return false;
+}
+EXPORT_SYMBOL(ns_task_capable);
+
 /**
  * ns_capable - Determine if the current task has a superior capability in effect
  * @ns:  The usernamespace we want the capability in
@@ -369,16 +393,7 @@ EXPORT_SYMBOL(capable);
  */
 bool ns_capable(struct user_namespace *ns, int cap)
 {
-	if (unlikely(!cap_valid(cap))) {
-		printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
-		BUG();
-	}
-
-	if (security_capable(ns, current_cred(), cap) == 0) {
-		current->flags |= PF_SUPERPRIV;
-		return true;
-	}
-	return false;
+	return ns_task_capable(current, ns, cap);
 }
 EXPORT_SYMBOL(ns_capable);
 
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 2df1157..df8fe32 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -132,9 +132,9 @@ int ptrace_check_attach(struct task_struct *child, int kill)
 	return ret;
 }
 
-int __ptrace_may_access(struct task_struct *task, unsigned int mode)
+int __ptrace_may_access(struct task_struct *who, struct task_struct *task, unsigned int mode)
 {
-	const struct cred *cred = current_cred(), *tcred;
+	const struct cred *cred, *tcred;
 
 	/* May we inspect the given task?
 	 * This check is used both for attaching with ptrace
@@ -149,6 +149,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 	if (task == current)
 		return 0;
 	rcu_read_lock();
+	cred = __task_cred(who);
 	tcred = __task_cred(task);
 	if (cred->user->user_ns == tcred->user->user_ns &&
 	    (cred->uid == tcred->euid &&
@@ -158,7 +159,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 	     cred->gid == tcred->sgid &&
 	     cred->gid == tcred->gid))
 		goto ok;
-	if (ns_capable(tcred->user->user_ns, CAP_SYS_PTRACE))
+	if (ns_task_capable(who, tcred->user->user_ns, CAP_SYS_PTRACE))
 		goto ok;
 	rcu_read_unlock();
 	return -EPERM;
@@ -167,17 +168,32 @@ ok:
 	smp_rmb();
 	if (task->mm)
 		dumpable = get_dumpable(task->mm);
-	if (!dumpable && !task_ns_capable(task, CAP_SYS_PTRACE))
+	if (!dumpable &&
+	    !ns_task_capable(who, task_cred_xxx(task, user)->user_ns,
+		 CAP_SYS_PTRACE))
 		return -EPERM;
 
-	return security_ptrace_access_check(task, mode);
+	return security_ptrace_task_access_check(who, task, mode);
 }
 
 bool ptrace_may_access(struct task_struct *task, unsigned int mode)
 {
 	int err;
 	task_lock(task);
-	err = __ptrace_may_access(task, mode);
+	err = __ptrace_may_access(current, task, mode);
+	task_unlock(task);
+	return !err;
+}
+
+/*
+ * Generic task_may_access_task cannot be implemented because we have to
+ * hold task_locks of both tasks.  It would lead to a deadlock.
+ */
+bool ptrace_task_may_access_current(struct task_struct *task, unsigned int mode)
+{
+	int err;
+	task_lock(task);
+	err = __ptrace_may_access(task, current, mode);
 	task_unlock(task);
 	return !err;
 }
@@ -205,7 +221,7 @@ static int ptrace_attach(struct task_struct *task)
 		goto out;
 
 	task_lock(task);
-	retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
+	retval = __ptrace_may_access(current, task, PTRACE_MODE_ATTACH);
 	task_unlock(task);
 	if (retval)
 		goto unlock_creds;
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index ec1bcec..dc3a4aa 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -93,14 +93,14 @@ static void apparmor_cred_transfer(struct cred *new, const struct cred *old)
 	aa_dup_task_context(new_cxt, old_cxt);
 }
 
-static int apparmor_ptrace_access_check(struct task_struct *child,
-					unsigned int mode)
+static int apparmor_ptrace_access_check(struct task_struct *task,
+			    struct task_struct *child, unsigned int mode)
 {
-	int error = cap_ptrace_access_check(child, mode);
+	int error = cap_ptrace_access_check(task, child, mode);
 	if (error)
 		return error;
 
-	return aa_ptrace(current, child, mode);
+	return aa_ptrace(task, child, mode);
 }
 
 static int apparmor_ptrace_traceme(struct task_struct *parent)
diff --git a/security/commoncap.c b/security/commoncap.c
index a93b3b7..31ca991 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -136,18 +136,19 @@ int cap_settime(const struct timespec *ts, const struct timezone *tz)
  * Determine whether a process may access another, returning 0 if permission
  * granted, -ve if denied.
  */
-int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
+int cap_ptrace_access_check(struct task_struct *task, struct task_struct *child,
+	unsigned int mode)
 {
 	int ret = 0;
 	const struct cred *cred, *child_cred;
 
 	rcu_read_lock();
-	cred = current_cred();
+	cred = __task_cred(task);
 	child_cred = __task_cred(child);
 	if (cred->user->user_ns == child_cred->user->user_ns &&
 	    cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
 		goto out;
-	if (ns_capable(child_cred->user->user_ns, CAP_SYS_PTRACE))
+	if (ns_task_capable(task, child_cred->user->user_ns, CAP_SYS_PTRACE))
 		goto out;
 	ret = -EPERM;
 out:
diff --git a/security/security.c b/security/security.c
index 4ba6d4c..0760e81 100644
--- a/security/security.c
+++ b/security/security.c
@@ -127,9 +127,15 @@ int __init register_security(struct security_operations *ops)
 
 /* Security operations */
 
+int security_ptrace_task_access_check(struct task_struct *task,
+		 struct task_struct *child, unsigned int mode)
+{
+	return security_ops->ptrace_access_check(task, child, mode);
+}
+
 int security_ptrace_access_check(struct task_struct *child, unsigned int mode)
 {
-	return security_ops->ptrace_access_check(child, mode);
+	return security_ops->ptrace_access_check(current, child, mode);
 }
 
 int security_ptrace_traceme(struct task_struct *parent)
@@ -154,11 +160,16 @@ int security_capset(struct cred *new, const struct cred *old,
 				    effective, inheritable, permitted);
 }
 
+int security_task_capable(struct task_struct *task, struct user_namespace *ns,
+	const struct cred *cred, int cap)
+{
+	return security_ops->capable(task, cred, ns, cap, SECURITY_CAP_AUDIT);
+}
+
 int security_capable(struct user_namespace *ns, const struct cred *cred,
 		     int cap)
 {
-	return security_ops->capable(current, cred, ns, cap,
-				     SECURITY_CAP_AUDIT);
+	return security_task_capable(current, ns, cred, cap);
 }
 
 int security_real_capable(struct task_struct *tsk, struct user_namespace *ns,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 20219ef..0130255 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1804,23 +1804,22 @@ static inline u32 open_file_to_av(struct file *file)
 }
 
 /* Hook functions begin here. */
-
-static int selinux_ptrace_access_check(struct task_struct *child,
-				     unsigned int mode)
+static int selinux_ptrace_access_check(struct task_struct *task,
+		struct task_struct *child, unsigned int mode)
 {
 	int rc;
 
-	rc = cap_ptrace_access_check(child, mode);
+	rc = cap_ptrace_access_check(task, child, mode);
 	if (rc)
 		return rc;
 
 	if (mode == PTRACE_MODE_READ) {
-		u32 sid = current_sid();
+		u32 sid = task_sid(task);
 		u32 csid = task_sid(child);
 		return avc_has_perm(sid, csid, SECCLASS_FILE, FILE__READ, NULL);
 	}
 
-	return current_has_perm(child, PROCESS__PTRACE);
+	return task_has_perm(task, child, PROCESS__PTRACE);
 }
 
 static int selinux_ptrace_traceme(struct task_struct *parent)
diff --git a/security/smack/smack.h b/security/smack/smack.h
index 2b6c6a5..4d9fb0f 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -199,6 +199,7 @@ struct inode_smack *new_inode_smack(char *);
  */
 int smk_access_entry(char *, char *, struct list_head *);
 int smk_access(char *, char *, int, struct smk_audit_info *);
+int smk_taskacc(struct task_struct *, char *, u32, struct smk_audit_info *);
 int smk_curacc(char *, u32, struct smk_audit_info *);
 int smack_to_cipso(const char *, struct smack_cipso *);
 void smack_from_cipso(u32, char *, char *);
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 9637e10..766dccd 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -201,7 +201,8 @@ out_audit:
 }
 
 /**
- * smk_curacc - determine if current has a specific access to an object
+ * smk_curacc - determine if subject has a specific access to an object
+ * @task: a pointer to the subject's task struct
  * @obj_label: a pointer to the object's Smack label
  * @mode: the access requested, in "MAY" format
  * @a : common audit data
@@ -211,9 +212,9 @@ out_audit:
  * non zero otherwise. It allows that current may have the capability
  * to override the rules.
  */
-int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
+int smk_taskacc(struct task_struct *task, char *obj_label, u32 mode, struct smk_audit_info *a)
 {
-	struct task_smack *tsp = current_security();
+	struct task_smack *tsp = task_cred_xxx(task, security);
 	char *sp = smk_of_task(tsp);
 	int may;
 	int rc;
@@ -243,7 +244,7 @@ int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
 	if (smack_onlycap != NULL && smack_onlycap != sp)
 		goto out_audit;
 
-	if (capable(CAP_MAC_OVERRIDE))
+	if (task_capable(task, CAP_MAC_OVERRIDE))
 		rc = 0;
 
 out_audit:
@@ -254,6 +255,22 @@ out_audit:
 	return rc;
 }
 
+/**
+ * smk_curacc - determine if current has a specific access to an object
+ * @obj_label: a pointer to the object's Smack label
+ * @mode: the access requested, in "MAY" format
+ * @a : common audit data
+ *
+ * This function checks the current subject label/object label pair
+ * in the access rule list and returns 0 if the access is permitted,
+ * non zero otherwise. It allows that current may have the capability
+ * to override the rules.
+ */
+int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
+{
+	return smk_taskacc(current, obj_label, mode, a);
+}
+
 #ifdef CONFIG_AUDIT
 /**
  * smack_str_from_perm : helper to transalate an int to a
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 9831a39..ee1c5cb 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -149,13 +149,14 @@ static int smk_copy_rules(struct list_head *nhead, struct list_head *ohead,
  *
  * Do the capability checks, and require read and write.
  */
-static int smack_ptrace_access_check(struct task_struct *ctp, unsigned int mode)
+static int smack_ptrace_access_check(struct task_struct *task,
+			struct task_struct *ctp, unsigned int mode)
 {
 	int rc;
 	struct smk_audit_info ad;
 	char *tsp;
 
-	rc = cap_ptrace_access_check(ctp, mode);
+	rc = cap_ptrace_access_check(task, ctp, mode);
 	if (rc != 0)
 		return rc;
 
@@ -163,7 +164,7 @@ static int smack_ptrace_access_check(struct task_struct *ctp, unsigned int mode)
 	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
 	smk_ad_setfield_u_tsk(&ad, ctp);
 
-	rc = smk_curacc(tsp, MAY_READWRITE, &ad);
+	rc = smk_taskacc(task, tsp, MAY_READWRITE, &ad);
 	return rc;
 }
 
---
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