[PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

From: Grzegorz Halat
Date: Fri Apr 26 2019 - 10:59:59 EST


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@xxxxxxxxxx>
---
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