new helper: iterate_fd()

iterates through the opened files in given descriptor table,
calling a supplied function; we stop once non-zero is returned.
Callback gets struct file *, descriptor number and const void *
argument passed to iterator.  It is called with files->file_lock
held, so it is not allowed to block.

tty_io, netprio_cgroup and selinux flush_unauthorized_files()
converted to its use.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 13 insertions, 23 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index b425c79675a..71d95cfbabe 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2791,6 +2791,13 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 }
 #endif
 
+static int this_tty(const void *t, struct file *file, unsigned fd)
+{
+	if (likely(file->f_op->read != tty_read))
+		return 0;
+	return file_tty(file) != t ? 0 : fd + 1;
+}
+	
 /*
  * This implements the "Secure Attention Key" ---  the idea is to
  * prevent trojan horses by killing all processes associated with this
@@ -2818,8 +2825,6 @@ void __do_SAK(struct tty_struct *tty)
 	struct task_struct *g, *p;
 	struct pid *session;
 	int		i;
-	struct file	*filp;
-	struct fdtable *fdt;
 
 	if (!tty)
 		return;
@@ -2849,27 +2854,12 @@ void __do_SAK(struct tty_struct *tty)
 			continue;
 		}
 		task_lock(p);
-		if (p->files) {
-			/*
-			 * We don't take a ref to the file, so we must
-			 * hold ->file_lock instead.
-			 */
-			spin_lock(&p->files->file_lock);
-			fdt = files_fdtable(p->files);
-			for (i = 0; i < fdt->max_fds; i++) {
-				filp = fcheck_files(p->files, i);
-				if (!filp)
-					continue;
-				if (filp->f_op->read == tty_read &&
-				    file_tty(filp) == tty) {
-					printk(KERN_NOTICE "SAK: killed process %d"
-					    " (%s): fd#%d opened to the tty\n",
-					    task_pid_nr(p), p->comm, i);
-					force_sig(SIGKILL, p);
-					break;
-				}
-			}
-			spin_unlock(&p->files->file_lock);
+		i = iterate_fd(p->files, 0, this_tty, tty);
+		if (i != 0) {
+			printk(KERN_NOTICE "SAK: killed process %d"
+			    " (%s): fd#%d opened to the tty\n",
+				    task_pid_nr(p), p->comm, i - 1);
+			force_sig(SIGKILL, p);
 		}
 		task_unlock(p);
 	} while_each_thread(g, p);