[kernel-hardening] [RFC v2] security: intoduce ptrace_task_may_access_current

Vasiliy Kulikov
2011-06-17T17:11:54Z

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@openwall.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;
}

---