[PATCH] use ptrace_get_task_struct in various places

The ptrace_get_task_struct() helper that I added as part of the ptrace
consolidation is useful in variety of places that currently opencode it.
Switch them to the common helpers.

Add a ptrace_traceme() helper that needs to be explicitly called, and simplify
the ptrace_get_task_struct() interface.  We don't need the request argument
now, and we return the task_struct directly, using ERR_PTR() for error
returns.  It's a bit more code in the callers, but we have two sane routines
that do one thing well now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 46 insertions, 31 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 656476eedb1b..cceaf09ac413 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -408,54 +408,62 @@ int ptrace_request(struct task_struct *child, long request,
         return ret;
 }
 
-#ifndef __ARCH_SYS_PTRACE
-static int ptrace_get_task_struct(long request, long pid,
-                struct task_struct **childp)
+/**
+ * ptrace_traceme  --  helper for PTRACE_TRACEME
+ *
+ * Performs checks and sets PT_PTRACED.
+ * Should be used by all ptrace implementations for PTRACE_TRACEME.
+ */
+int ptrace_traceme(void)
 {
-        struct task_struct *child;
         int ret;
 
         /*
-         * Callers use child == NULL as an indication to exit early even
-         * when the return value is 0, so make sure it is non-NULL here.
+         * Are we already being traced?
+         */
+        if (current->ptrace & PT_PTRACED)
+                return -EPERM;
+        ret = security_ptrace(current->parent, current);
+        if (ret)
+                return -EPERM;
+        /*
+         * Set the ptrace bit in the process ptrace flags.
          */
-        *childp = NULL;
+        current->ptrace |= PT_PTRACED;
+        return 0;
+}
 
-        if (request == PTRACE_TRACEME) {
-                /*
-                 * Are we already being traced?
-                 */
-                if (current->ptrace & PT_PTRACED)
-                        return -EPERM;
-                ret = security_ptrace(current->parent, current);
-                if (ret)
-                        return -EPERM;
-                /*
-                 * Set the ptrace bit in the process ptrace flags.
-                 */
-                current->ptrace |= PT_PTRACED;
-                return 0;
-        }
+/**
+ * ptrace_get_task_struct  --  grab a task struct reference for ptrace
+ * @pid:       process id to grab a task_struct reference of
+ *
+ * This function is a helper for ptrace implementations.  It checks
+ * permissions and then grabs a task struct for use of the actual
+ * ptrace implementation.
+ *
+ * Returns the task_struct for @pid or an ERR_PTR() on failure.
+ */
+struct task_struct *ptrace_get_task_struct(pid_t pid)
+{
+        struct task_struct *child;
 
         /*
-         * You may not mess with init
+         * Tracing init is not allowed.
          */
         if (pid == 1)
-                return -EPERM;
+                return ERR_PTR(-EPERM);
 
-        ret = -ESRCH;
         read_lock(&tasklist_lock);
         child = find_task_by_pid(pid);
         if (child)
                 get_task_struct(child);
         read_unlock(&tasklist_lock);
         if (!child)
-                return -ESRCH;
-
-        *childp = child;
-        return 0;
+                return ERR_PTR(-ESRCH);
+        return child;
 }
 
+#ifndef __ARCH_SYS_PTRACE
 asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
 {
         struct task_struct *child;
@@ -465,9 +473,16 @@ asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
          * This lock_kernel fixes a subtle race with suid exec
          */
         lock_kernel();
-        ret = ptrace_get_task_struct(request, pid, &child);
-        if (!child)
+        if (request == PTRACE_TRACEME) {
+                ret = ptrace_traceme();
                 goto out;
+        }
+
+        child = ptrace_get_task_struct(pid);
+        if (IS_ERR(child)) {
+                ret = PTR_ERR(child);
+                goto out;
+        }
 
         if (request == PTRACE_ATTACH) {
                 ret = ptrace_attach(child);