linux-kernel - [PATCH 3.12 004/142] proc: actually make proc_fd

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Message-Id: <71755056d169833625addb418e59e2b2d8d3bcdf.1456308281.git.jslaby@suse.cz>
Date:	Wed, 24 Feb 2016 11:03:19 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 004/142] proc: actually make proc_fd_permission() thread-friendly

From: Oleg Nesterov <oleg@...hat.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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).

Fixes: 96d0df79f264 ("proc: make proc_fd_permission() thread-friendly")
Reported-by: "Jin, Yihua" <yihua.jin@...el.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/proc/fd.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 985ea881b5bc..c06a1f97ac22 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -283,11 +283,19 @@ static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
  */
 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;
 }
 
-- 
2.7.1