proc: actually make proc_fd_permission() thread-friendly

PATCH New Oleg Nesterov 1 participant 1 message Nov 3, 2015 Proc filesystem

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Oleg Nesterov

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2015-11-03 16:42 UTC #0 lore raw

PATCH 1/1 proc: actually make proc_fd_permission() thread-friendly

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).

Reported-by "Jin, Yihua" <[email protected]>

Signed-off-by Oleg Nesterov <[email protected]>

Cc [email protected]

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

fs/proc/fd.c +11 -3

index 6e5fcd0..3c2a915 100644
@@ -291,11 +291,19 @@ 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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