VT ioctl race fix

PATCH New Samuel Ortiz 1 participant 1 message Sep 27, 2007 Char and misc drivers

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Samuel Ortiz

author

2007-09-27 10:03 UTC #0 lore raw

PATCH 1/1 VT ioctl race fix

Hi,

When calling the RELDISP VT ioctl, we are reading vt_newvt while the console workqueue could be messing with it (through change_console()). We fix this race by taking the console semaphore before reading vt_newvt.

Andrew, would you please consider this patch for -mm inclusion ?

Signed-off-by Samuel Ortiz <[email protected]>

---
 drivers/char/vt_ioctl.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

drivers/char/vt_ioctl.c +5 -3

Index: linux-2.6.22/drivers/char/vt_ioctl.c
===================================================================
@@ -770,6 +770,7 @@
 		/*
 		 * Switching-from response
 		 */
+		acquire_console_sem();
 		if (vc->vt_newvt >= 0) {
 			if (arg == 0)
 				/*

@@ -784,7 +785,6 @@
 				 * complete the switch.
 				 */
 				int newvt;
-				acquire_console_sem();
 				newvt = vc->vt_newvt;
 				vc->vt_newvt = -1;
 				i = vc_allocate(newvt);

@@ -798,7 +798,6 @@
 				 * other console switches..
 				 */
 				complete_change_console(vc_cons[newvt].d);
-				release_console_sem();
 			}
 		}

@@ -810,9 +809,12 @@
 			/*
 			 * If it's just an ACK, ignore it
 			 */
-			if (arg != VT_ACKACQ)
+			if (arg != VT_ACKACQ) {
+				release_console_sem();
 				return -EINVAL;
+			}
 		}
+		release_console_sem();
 
 		return 0;