security: Fix setting of PF_SUPERPRIV by __capable()

Fix the setting of PF_SUPERPRIV by __capable() as it could corrupt the flags
the target process if that is not the current process and it is trying to
change its own flags in a different way at the same time.

__capable() is using neither atomic ops nor locking to protect t->flags.  This
patch removes __capable() and introduces has_capability() that doesn't set
PF_SUPERPRIV on the process being queried.

This patch further splits security_ptrace() in two:

 (1) security_ptrace_may_access().  This passes judgement on whether one
     process may access another only (PTRACE_MODE_ATTACH for ptrace() and
     PTRACE_MODE_READ for /proc), and takes a pointer to the child process.
     current is the parent.

 (2) security_ptrace_traceme().  This passes judgement on PTRACE_TRACEME only,
     and takes only a pointer to the parent process.  current is the child.

     In Smack and commoncap, this uses has_capability() to determine whether
     the parent will be permitted to use PTRACE_ATTACH if normal checks fail.
     This does not set PF_SUPERPRIV.

Two of the instances of __capable() actually only act on current, and so have
been changed to calls to capable().

Of the places that were using __capable():

 (1) The OOM killer calls __capable() thrice when weighing the killability of a
     process.  All of these now use has_capability().

 (2) cap_ptrace() and smack_ptrace() were using __capable() to check to see
     whether the parent was allowed to trace any process.  As mentioned above,
     these have been split.  For PTRACE_ATTACH and /proc, capable() is now
     used, and for PTRACE_TRACEME, has_capability() is used.

 (3) cap_safe_nice() only ever saw current, so now uses capable().

 (4) smack_setprocattr() rejected accesses to tasks other than current just
     after calling __capable(), so the order of these two tests have been
     switched and capable() is used instead.

 (5) In smack_file_send_sigiotask(), we need to allow privileged processes to
     receive SIGIO on files they're manipulating.

 (6) In smack_task_wait(), we let a process wait for a privileged process,
     whether or not the process doing the waiting is privileged.

I've tested this with the LTP SELinux and syscalls testscripts.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: James Morris <jmorris@namei.org>

11 files changed, 137 insertions, 63 deletions

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 02673846d205..9d1fe30b6f6c 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -503,8 +503,19 @@ extern const kernel_cap_t __cap_init_eff_set;
 
 kernel_cap_t cap_set_effective(const kernel_cap_t pE_new);
 
-int capable(int cap);
-int __capable(struct task_struct *t, int cap);
+/**
+ * has_capability - Determine if a task has a superior capability available
+ * @t: The task in question
+ * @cap: The capability to be tested for
+ *
+ * Return true if the specified task has the given superior capability
+ * currently in effect, false if not.
+ *
+ * Note that this does not set PF_SUPERPRIV on the task.
+ */
+#define has_capability(t, cap) (security_capable((t), (cap)) == 0)
+
+extern int capable(int cap);
 
 #endif /* __KERNEL__ */
 
diff --git a/include/linux/security.h b/include/linux/security.h
index fd96e7f8a6f9..2ee5ecfb2393 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -46,8 +46,8 @@ struct audit_krule;
  */
 extern int cap_capable(struct task_struct *tsk, int cap);
 extern int cap_settime(struct timespec *ts, struct timezone *tz);
-extern int cap_ptrace(struct task_struct *parent, struct task_struct *child,
-                      unsigned int mode);
+extern int cap_ptrace_may_access(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_check(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted);
 extern void cap_capset_set(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted);
@@ -1157,17 +1157,24 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *      @alter contains the flag indicating whether changes are to be made.
  *      Return 0 if permission is granted.
  *
- * @ptrace:
- *      Check permission before allowing the @parent process to trace the
+ * @ptrace_may_access:
+ *      Check permission before allowing the current process to trace the
  *      @child process.
  *      Security modules may also want to perform a process tracing check
  *      during an execve in the set_security or apply_creds hooks of
  *      binprm_security_ops if the process is being traced and its security
  *      attributes would be changed by the execve.
- *      @parent contains the task_struct structure for parent process.
- *      @child contains the task_struct structure for child process.
+ *      @child contains the task_struct structure for the target process.
  *      @mode contains the PTRACE_MODE flags indicating the form of access.
  *      Return 0 if permission is granted.
+ * @ptrace_traceme:
+ *      Check that the @parent process has sufficient permission to trace the
+ *      current process before allowing the current process to present itself
+ *      to the @parent process for tracing.
+ *      The parent process will still have to undergo the ptrace_may_access
+ *      checks before it is allowed to trace this one.
+ *      @parent contains the task_struct structure for debugger process.
+ *      Return 0 if permission is granted.
  * @capget:
  *      Get the @effective, @inheritable, and @permitted capability sets for
  *      the @target process.  The hook may also perform permission checking to
@@ -1287,8 +1294,8 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
 struct security_operations {
         char name[SECURITY_NAME_MAX + 1];
 
-        int (*ptrace) (struct task_struct *parent, struct task_struct *child,
-                       unsigned int mode);
+        int (*ptrace_may_access) (struct task_struct *child, unsigned int mode);
+        int (*ptrace_traceme) (struct task_struct *parent);
         int (*capget) (struct task_struct *target,
                        kernel_cap_t *effective,
                        kernel_cap_t *inheritable, kernel_cap_t *permitted);
@@ -1560,8 +1567,8 @@ extern struct dentry *securityfs_create_dir(const char *name, struct dentry *par
 extern void securityfs_remove(struct dentry *dentry);
 
 /* Security operations */
-int security_ptrace(struct task_struct *parent, struct task_struct *child,
-                    unsigned int mode);
+int security_ptrace_may_access(struct task_struct *child, unsigned int mode);
+int security_ptrace_traceme(struct task_struct *parent);
 int security_capget(struct task_struct *target,
                     kernel_cap_t *effective,
                     kernel_cap_t *inheritable,
@@ -1742,11 +1749,15 @@ static inline int security_init(void)
         return 0;
 }
 
-static inline int security_ptrace(struct task_struct *parent,
-                                  struct task_struct *child,
-                                  unsigned int mode)
+static inline int security_ptrace_may_access(struct task_struct *child,
+                                             unsigned int mode)
+{
+        return cap_ptrace_may_access(child, mode);
+}
+
+static inline int security_ptrace_traceme(struct task_struct *child)
 {
-        return cap_ptrace(parent, child, mode);
+        return cap_ptrace_traceme(parent);
 }
 
 static inline int security_capget(struct task_struct *target,
diff --git a/kernel/capability.c b/kernel/capability.c
index 0101e847603e..33e51e78c2d8 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -486,17 +486,22 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
         return ret;
 }
 
-int __capable(struct task_struct *t, int cap)
+/**
+ * capable - Determine if the current task has a superior capability in effect
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+int capable(int cap)
 {
-        if (security_capable(t, cap) == 0) {
-                t->flags |= PF_SUPERPRIV;
+        if (has_capability(current, cap)) {
+                current->flags |= PF_SUPERPRIV;
                 return 1;
         }
         return 0;
 }
-
-int capable(int cap)
-{
-        return __capable(current, cap);
-}
 EXPORT_SYMBOL(capable);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 082b3fcb32a0..356699a96d56 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -140,7 +140,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
         if (!dumpable && !capable(CAP_SYS_PTRACE))
                 return -EPERM;
 
-        return security_ptrace(current, task, mode);
+        return security_ptrace_may_access(task, mode);
 }
 
 bool ptrace_may_access(struct task_struct *task, unsigned int mode)
@@ -499,8 +499,7 @@ repeat:
                         goto repeat;
                 }
 
-                ret = security_ptrace(current->parent, current,
-                                      PTRACE_MODE_ATTACH);
+                ret = security_ptrace_traceme(current->parent);
 
                 /*
                  * Set the ptrace bit in the process ptrace flags.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8a5467ee6265..64e5b4bcd964 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -26,6 +26,7 @@
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/memcontrol.h>
+#include <linux/security.h>
 
 int sysctl_panic_on_oom;
 int sysctl_oom_kill_allocating_task;
@@ -128,7 +129,8 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
          * Superuser processes are usually more important, so we make it
          * less likely that we kill those.
          */
-        if (__capable(p, CAP_SYS_ADMIN) || __capable(p, CAP_SYS_RESOURCE))
+        if (has_capability(p, CAP_SYS_ADMIN) ||
+            has_capability(p, CAP_SYS_RESOURCE))
                 points /= 4;
 
         /*
@@ -137,7 +139,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
          * tend to only have this flag set on applications they think
          * of as important.
          */
-        if (__capable(p, CAP_SYS_RAWIO))
+        if (has_capability(p, CAP_SYS_RAWIO))
                 points /= 4;
 
         /*
diff --git a/security/capability.c b/security/capability.c
index 63d10da515a5..245874819036 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -811,7 +811,8 @@ struct security_operations default_security_ops = {
 
 void security_fixup_ops(struct security_operations *ops)
 {
-        set_to_cap_if_null(ops, ptrace);
+        set_to_cap_if_null(ops, ptrace_may_access);
+        set_to_cap_if_null(ops, ptrace_traceme);
         set_to_cap_if_null(ops, capget);
         set_to_cap_if_null(ops, capset_check);
         set_to_cap_if_null(ops, capset_set);
diff --git a/security/commoncap.c b/security/commoncap.c
index 4afbece37a08..e4c4b3fc0c04 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -63,14 +63,24 @@ int cap_settime(struct timespec *ts, struct timezone *tz)
         return 0;
 }
 
-int cap_ptrace (struct task_struct *parent, struct task_struct *child,
-                unsigned int mode)
+int cap_ptrace_may_access(struct task_struct *child, unsigned int mode)
 {
         /* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
-        if (!cap_issubset(child->cap_permitted, parent->cap_permitted) &&
-            !__capable(parent, CAP_SYS_PTRACE))
-                return -EPERM;
-        return 0;
+        if (cap_issubset(child->cap_permitted, current->cap_permitted))
+                return 0;
+        if (capable(CAP_SYS_PTRACE))
+                return 0;
+        return -EPERM;
+}
+
+int cap_ptrace_traceme(struct task_struct *parent)
+{
+        /* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
+        if (cap_issubset(current->cap_permitted, parent->cap_permitted))
+                return 0;
+        if (has_capability(parent, CAP_SYS_PTRACE))
+                return 0;
+        return -EPERM;
 }
 
 int cap_capget (struct task_struct *target, kernel_cap_t *effective,
@@ -534,7 +544,7 @@ int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
 static inline int cap_safe_nice(struct task_struct *p)
 {
         if (!cap_issubset(p->cap_permitted, current->cap_permitted) &&
-            !__capable(current, CAP_SYS_NICE))
+            !capable(CAP_SYS_NICE))
                 return -EPERM;
         return 0;
 }
diff --git a/security/root_plug.c b/security/root_plug.c
index be0ebec2580b..c3f68b5b372d 100644
--- a/security/root_plug.c
+++ b/security/root_plug.c
@@ -72,7 +72,8 @@ static int rootplug_bprm_check_security (struct linux_binprm *bprm)
 
 static struct security_operations rootplug_security_ops = {
         /* Use the capability functions for some of the hooks */
-        .ptrace =                       cap_ptrace,
+        .ptrace_may_access =            cap_ptrace_may_access,
+        .ptrace_traceme =               cap_ptrace_traceme,
         .capget =                       cap_capget,
         .capset_check =                 cap_capset_check,
         .capset_set =                   cap_capset_set,
diff --git a/security/security.c b/security/security.c
index ff7068727757..3a4b4f55b33f 100644
--- a/security/security.c
+++ b/security/security.c
@@ -127,10 +127,14 @@ int register_security(struct security_operations *ops)
 
 /* Security operations */
 
-int security_ptrace(struct task_struct *parent, struct task_struct *child,
-                    unsigned int mode)
+int security_ptrace_may_access(struct task_struct *child, unsigned int mode)
 {
-        return security_ops->ptrace(parent, child, mode);
+        return security_ops->ptrace_may_access(child, mode);
+}
+
+int security_ptrace_traceme(struct task_struct *parent)
+{
+        return security_ops->ptrace_traceme(parent);
 }
 
 int security_capget(struct task_struct *target,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 3ae9bec5a508..03fc6a81ae32 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1738,24 +1738,34 @@ static inline u32 file_to_av(struct file *file)
 
 /* Hook functions begin here. */
 
-static int selinux_ptrace(struct task_struct *parent,
-                          struct task_struct *child,
-                          unsigned int mode)
+static int selinux_ptrace_may_access(struct task_struct *child,
+                                     unsigned int mode)
 {
         int rc;
 
-        rc = secondary_ops->ptrace(parent, child, mode);
+        rc = secondary_ops->ptrace_may_access(child, mode);
         if (rc)
                 return rc;
 
         if (mode == PTRACE_MODE_READ) {
-                struct task_security_struct *tsec = parent->security;
+                struct task_security_struct *tsec = current->security;
                 struct task_security_struct *csec = child->security;
                 return avc_has_perm(tsec->sid, csec->sid,
                                     SECCLASS_FILE, FILE__READ, NULL);
         }
 
-        return task_has_perm(parent, child, PROCESS__PTRACE);
+        return task_has_perm(current, child, PROCESS__PTRACE);
+}
+
+static int selinux_ptrace_traceme(struct task_struct *parent)
+{
+        int rc;
+
+        rc = secondary_ops->ptrace_traceme(parent);
+        if (rc)
+                return rc;
+
+        return task_has_perm(parent, current, PROCESS__PTRACE);
 }
 
 static int selinux_capget(struct task_struct *target, kernel_cap_t *effective,
@@ -5346,7 +5356,8 @@ static int selinux_key_getsecurity(struct key *key, char **_buffer)
 static struct security_operations selinux_ops = {
         .name =                         "selinux",
 
-        .ptrace =                       selinux_ptrace,
+        .ptrace_may_access =            selinux_ptrace_may_access,
+        .ptrace_traceme =               selinux_ptrace_traceme,
         .capget =                       selinux_capget,
         .capset_check =                 selinux_capset_check,
         .capset_set =                   selinux_capset_set,
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 1b40e558f983..87d75417ea93 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -87,27 +87,46 @@ struct inode_smack *new_inode_smack(char *smack)
  */
 
 /**
- * smack_ptrace - Smack approval on ptrace
- * @ptp: parent task pointer
+ * smack_ptrace_may_access - Smack approval on PTRACE_ATTACH
  * @ctp: child task pointer
  *
  * Returns 0 if access is OK, an error code otherwise
  *
  * Do the capability checks, and require read and write.
  */
-static int smack_ptrace(struct task_struct *ptp, struct task_struct *ctp,
-                        unsigned int mode)
+static int smack_ptrace_may_access(struct task_struct *ctp, unsigned int mode)
 {
         int rc;
 
-        rc = cap_ptrace(ptp, ctp, mode);
+        rc = cap_ptrace_may_access(ctp, mode);
         if (rc != 0)
                 return rc;
 
-        rc = smk_access(ptp->security, ctp->security, MAY_READWRITE);
-        if (rc != 0 && __capable(ptp, CAP_MAC_OVERRIDE))
+        rc = smk_access(current->security, ctp->security, MAY_READWRITE);
+        if (rc != 0 && capable(CAP_MAC_OVERRIDE))
                 return 0;
+        return rc;
+}
+
+/**
+ * smack_ptrace_traceme - Smack approval on PTRACE_TRACEME
+ * @ptp: parent task pointer
+ *
+ * Returns 0 if access is OK, an error code otherwise
+ *
+ * Do the capability checks, and require read and write.
+ */
+static int smack_ptrace_traceme(struct task_struct *ptp)
+{
+        int rc;
+
+        rc = cap_ptrace_traceme(ptp);
+        if (rc != 0)
+                return rc;
 
+        rc = smk_access(ptp->security, current->security, MAY_READWRITE);
+        if (rc != 0 && has_capability(ptp, CAP_MAC_OVERRIDE))
+                return 0;
         return rc;
 }
 
@@ -923,7 +942,7 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
          */
         file = container_of(fown, struct file, f_owner);
         rc = smk_access(file->f_security, tsk->security, MAY_WRITE);
-        if (rc != 0 && __capable(tsk, CAP_MAC_OVERRIDE))
+        if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
                 return 0;
         return rc;
 }
@@ -1164,12 +1183,12 @@ static int smack_task_wait(struct task_struct *p)
          * account for the smack labels having gotten to
          * be different in the first place.
          *
-         * This breaks the strict subjet/object access
+         * This breaks the strict subject/object access
          * control ideal, taking the object's privilege
          * state into account in the decision as well as
          * the smack value.
          */
-        if (capable(CAP_MAC_OVERRIDE) || __capable(p, CAP_MAC_OVERRIDE))
+        if (capable(CAP_MAC_OVERRIDE) || has_capability(p, CAP_MAC_OVERRIDE))
                 return 0;
 
         return rc;
@@ -2016,9 +2035,6 @@ static int smack_setprocattr(struct task_struct *p, char *name,
 {
         char *newsmack;
 
-        if (!__capable(p, CAP_MAC_ADMIN))
-                return -EPERM;
-
         /*
          * Changing another process' Smack value is too dangerous
          * and supports no sane use case.
@@ -2026,6 +2042,9 @@ static int smack_setprocattr(struct task_struct *p, char *name,
         if (p != current)
                 return -EPERM;
 
+        if (!capable(CAP_MAC_ADMIN))
+                return -EPERM;
+
         if (value == NULL || size == 0 || size >= SMK_LABELLEN)
                 return -EINVAL;
 
@@ -2552,7 +2571,8 @@ static void smack_release_secctx(char *secdata, u32 seclen)
 struct security_operations smack_ops = {
         .name =                         "smack",
 
-        .ptrace =                       smack_ptrace,
+        .ptrace_may_access =            smack_ptrace_may_access,
+        .ptrace_traceme =               smack_ptrace_traceme,
         .capget =                       cap_capget,
         .capset_check =                 cap_capset_check,
         .capset_set =                   cap_capset_set,
@@ -2729,4 +2749,3 @@ static __init int smack_init(void)
  * all processes and objects when they are created.
  */
 security_initcall(smack_init);
-