[PATCH] fbcon: fix null-ptr-deref in fbcon_switch

[Qiujun Huang]

Add check for vc_cons[logo_shown].d, as it can be released by
vt_ioctl(VT_DISALLOCATE).

Reported-by: syzbot+732528bae351682f1f27 at syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain at gmail.com>
---
 drivers/video/fbdev/core/fbcon.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index bb6ae995c2e5..7ee0f7b55829 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2254,7 +2254,7 @@ static int fbcon_switch(struct vc_data *vc)
 		fbcon_update_softback(vc);
 	}
 
-	if (logo_shown >= 0) {
+	if (logo_shown >= 0 && vc_cons_allocated(logo_shown)) {
 		struct vc_data *conp2 = vc_cons[logo_shown].d;
 
 		if (conp2->vc_top == logo_lines
@@ -2852,7 +2852,7 @@ static void fbcon_scrolldelta(struct vc_data *vc, int lines)
 			return;
 		if (vc->vc_mode != KD_TEXT || !lines)
 			return;
-		if (logo_shown >= 0) {
+		if (logo_shown >= 0 && vc_cons_allocated(logo_shown)) {
 			struct vc_data *conp2 = vc_cons[logo_shown].d;
 
 			if (conp2->vc_top == logo_lines
-- 
2.17.1