[PATCH] introduce get_task_pid() to fix unsafe get_pid()

proc_pid_make_inode: ei->pid = get_pid(task_pid(task)); I think this is not safe. get_pid() can be preempted after checking "pid != NULL". Then the task exits, does detach_pid(), and RCU frees the pid. Signed-off-by: Oleg Nesterov <[email protected]> Cc: "Eric W. Biederman" <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
milouk · Oct 2, 2006 · 1a657f7 · 1a657f7
1 parent 1c0d04c
commit 1a657f7
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Showing 3 changed files with 13 additions and 2 deletions.
diff --git a/fs/proc/base.c b/fs/proc/base.c
@@ -958,7 +958,7 @@ static struct inode *proc_pid_make_inode(struct super_block * sb, struct task_st
 	/*
 	 * grab the reference to task.
 	 */
-	ei->pid = get_pid(task_pid(task));
+	ei->pid = get_task_pid(task, PIDTYPE_PID);
 	if (!ei->pid)
 		goto out_unlock;
 
@@ -1677,7 +1677,7 @@ static struct dentry *proc_base_instantiate(struct inode *dir,
 	/*
 	 * grab the reference to the task.
 	 */
-	ei->pid = get_pid(task_pid(task));
+	ei->pid = get_task_pid(task, PIDTYPE_PID);
 	if (!ei->pid)
 		goto out_iput;
 

diff --git a/include/linux/pid.h b/include/linux/pid.h
@@ -68,6 +68,8 @@ extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
 extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
 						enum pid_type));
 
+extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
+
 /*
  * attach_pid() and detach_pid() must be called with the tasklist_lock
  * write-held.

diff --git a/kernel/pid.c b/kernel/pid.c
@@ -304,6 +304,15 @@ struct task_struct *find_task_by_pid_type(int type, int nr)
 
 EXPORT_SYMBOL(find_task_by_pid_type);
 
+struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
+{
+	struct pid *pid;
+	rcu_read_lock();
+	pid = get_pid(task->pids[type].pid);
+	rcu_read_unlock();
+	return pid;
+}
+
 struct task_struct *fastcall get_pid_task(struct pid *pid, enum pid_type type)
 {
 	struct task_struct *result;