[PATCH] procfs: Fix listing of /proc/NOT_A_TGID/task

Listing /proc/PID/task were PID is not a TGID should not result in
duplicated entries.

	[g ~]$ pidof thunderbird-bin
	2751
	[g ~]$ ls /proc/2751/task
	2751  2770  2771  2824  2826  2834  2835  2851  2853
	[g ~]$ ls /proc/2770/task
	2751  2770  2771  2824  2826  2834  2835  2851  2853
	2770  2771  2824  2826  2834  2835  2851  2853
	[g ~]$

Signed-off-by: Guillaume Chazarain <guichaz@yahoo.fr>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ff7a66850602..1a979ea3b379 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2328,13 +2328,23 @@ static int proc_task_readdir(struct file * filp, void * dirent, filldir_t filldi
 {
         struct dentry *dentry = filp->f_path.dentry;
         struct inode *inode = dentry->d_inode;
-        struct task_struct *leader = get_proc_task(inode);
+        struct task_struct *leader = NULL;
         struct task_struct *task;
         int retval = -ENOENT;
         ino_t ino;
         int tid;
         unsigned long pos = filp->f_pos;  /* avoiding "long long" filp->f_pos */
 
+        task = get_proc_task(inode);
+        if (!task)
+                goto out_no_task;
+        rcu_read_lock();
+        if (pid_alive(task)) {
+                leader = task->group_leader;
+                get_task_struct(leader);
+        }
+        rcu_read_unlock();
+        put_task_struct(task);
         if (!leader)
                 goto out_no_task;
         retval = 0;