Patch "proc: actually make proc_fd_permission() thread-friendly" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

proc: actually make proc_fd_permission() thread-friendly

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
proc-actually-make-proc_fd_permission-thread-friendly.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Oleg Nesterov <[email protected]>
Date: Fri, 6 Nov 2015 16:30:06 -0800
Subject: proc: actually make proc_fd_permission() thread-friendly

From: Oleg Nesterov <[email protected]>

commit 54708d2858e79a2bdda10bf8a20c80eb96c20613 upstream.

The commit 96d0df79f264 ("proc: make proc_fd_permission() thread-friendly") fixed the access to /proc/self/fd from sub-threads, but introduced another
problem: a sub-thread can't access /proc/<tid>/fd/ or /proc/thread-self/fd if generic_permission() fails.

Change proc_fd_permission() to check same_thread_group(pid_task(), current).

---
 fs/proc/fd.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

@@ -291,11 +291,19 @@ static struct dentry *proc_lookupfd(stru
  */
 int proc_fd_permission(struct inode *inode, int mask)
 {
-	int rv = generic_permission(inode, mask);
+	struct task_struct *p;
+	int rv;
+
+	rv = generic_permission(inode, mask);
 	if (rv == 0)
-		return 0;
-	if (task_tgid(current) == proc_pid(inode))
+		return rv;
+
+	rcu_read_lock();
+	p = pid_task(proc_pid(inode), PIDTYPE_PID);
+	if (p && same_thread_group(p, current))
 		rv = 0;
+	rcu_read_unlock();
+
 	return rv;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/proc-actually-make-proc_fd_permission-thread-friendly.patch queue-4.3/kernel-signal.c-unexport-sigsuspend.patch