redo locking of tty->pgrp

Historically tty->pgrp and friends were pid_t and the code "knew" they were
safe.  The change to pid structs opened up a few races and the removal of the
BKL in places made them quite hittable.  We put tty->pgrp under the ctrl_lock
for the tty.

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/char/vt.c b/drivers/char/vt.c
index e64f0bf3624e..c71d1d0f13b9 100644
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -909,15 +909,21 @@ int vc_resize(struct vc_data *vc, unsigned int cols, unsigned int lines)
 
         if (vc->vc_tty) {
                 struct winsize ws, *cws = &vc->vc_tty->winsize;
+                unsigned long flags;
 
                 memset(&ws, 0, sizeof(ws));
                 ws.ws_row = vc->vc_rows;
                 ws.ws_col = vc->vc_cols;
                 ws.ws_ypixel = vc->vc_scan_lines;
+
+                mutex_lock(&vc->vc_tty->termios_mutex);
+                spin_lock_irqsave(&vc->vc_tty->ctrl_lock, flags);
                 if ((ws.ws_row != cws->ws_row || ws.ws_col != cws->ws_col) &&
                     vc->vc_tty->pgrp)
                         kill_pgrp(vc->vc_tty->pgrp, SIGWINCH, 1);
+                spin_unlock_irqrestore(&vc->vc_tty->ctrl_lock, flags);
                 *cws = ws;
+                mutex_unlock(&vc->vc_tty->termios_mutex);
         }
 
         if (CON_IS_VISIBLE(vc))