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Subject[PATCH 3.16.y-ckt 066/126] proc: actually make proc_fd_permission() thread-friendly
Date
3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@redhat.com>

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@intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
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 0788d093f5d8..f1073ea64b41 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -285,11 +285,19 @@ 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;
}


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