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>

1 files changed, 18 insertions, 7 deletions

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,