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From:   Grzegorz Halat <ghalat@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, linux-fbdev@vger.kernel.org,
        Oleksandr Natalenko <oleksandr@redhat.com>,
        Grzegorz Halat <ghalat@redhat.com>
Subject: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation
Date:   Fri, 26 Apr 2019 16:59:46 +0200
Message-Id: <20190426145946.26537-1-ghalat@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

After memory allocation failure vc_allocate() doesn't clean up data
which has been initialized in visual_init(). In case of fbcon this
leads to divide-by-0 in fbcon_init() on next open of the same tty.

memory allocation in vc_allocate() may fail here:
1097:     vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_KERNEL);

on next open() fbcon_init() skips vc_font.data initialization:
1088:     if (!p->fontdata) {

division by zero in fbcon_init() happens here:
1149:     new_cols /= vc->vc_font.width;

Additional check is needed in fbcon_deinit() to prevent
usage of uninitialized vc_screenbuf:

1251:        if (vc->vc_hi_font_mask && vc->vc_screenbuf)
1252:                set_vc_hi_font(vc, false);

Crash:

 #6 [ffffc90001eafa60] divide_error at ffffffff81a00be4
    [exception RIP: fbcon_init+463]
    RIP: ffffffff814b860f  RSP: ffffc90001eafb18  RFLAGS: 00010246
...
 #7 [ffffc90001eafb60] visual_init at ffffffff8154c36e
 #8 [ffffc90001eafb80] vc_allocate at ffffffff8154f53c
 #9 [ffffc90001eafbc8] con_install at ffffffff8154f624
...

Signed-off-by: Grzegorz Halat <ghalat@redhat.com>
---
 drivers/tty/vt/vt.c              | 11 +++++++++--
 drivers/video/fbdev/core/fbcon.c |  2 +-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 650c66886c80..ec85d195678f 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1056,6 +1056,13 @@ static void visual_init(struct vc_data *vc, int num, int init)
 	vc->vc_screenbuf_size = vc->vc_rows * vc->vc_size_row;
 }
 
+
+static void visual_deinit(struct vc_data *vc)
+{
+	vc->vc_sw->con_deinit(vc);
+	module_put(vc->vc_sw->owner);
+}
+
 int vc_allocate(unsigned int currcons)	/* return 0 on success */
 {
 	struct vt_notifier_param param;
@@ -1103,6 +1110,7 @@ int vc_allocate(unsigned int currcons)	/* return 0 on success */
 
 	return 0;
 err_free:
+	visual_deinit(vc);
 	kfree(vc);
 	vc_cons[currcons].d = NULL;
 	return -ENOMEM;
@@ -1331,9 +1339,8 @@ struct vc_data *vc_deallocate(unsigned int currcons)
 		param.vc = vc = vc_cons[currcons].d;
 		atomic_notifier_call_chain(&vt_notifier_list, VT_DEALLOCATE, &param);
 		vcs_remove_sysfs(currcons);
-		vc->vc_sw->con_deinit(vc);
+		visual_deinit(vc);
 		put_pid(vc->vt_pid);
-		module_put(vc->vc_sw->owner);
 		vc_uniscr_set(vc, NULL);
 		kfree(vc->vc_screenbuf);
 		vc_cons[currcons].d = NULL;
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index cd059a801662..c59b23f6e9ba 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1248,7 +1248,7 @@ static void fbcon_deinit(struct vc_data *vc)
 	if (free_font)
 		vc->vc_font.data = NULL;
 
-	if (vc->vc_hi_font_mask)
+	if (vc->vc_hi_font_mask && vc->vc_screenbuf)
 		set_vc_hi_font(vc, false);
 
 	if (!con_is_bound(&fb_con))
-- 
2.20.1