vt/fbcon: deinitialize resources in visual_init() after failed memory allocation [Linux 5.2]

vt/fbcon: deinitialize resources in visual_init() after failed memory allocation [Linux 5.2]

This Linux kernel change "vt/fbcon: deinitialize resources in visual_init() after failed memory allocation" is included in the Linux 5.2 release. This change is authored by Grzegorz Halat <ghalat [at] redhat.com> on Fri Apr 26 16:59:46 2019 +0200. The commit for this change in Linux stable tree is a1ad1cc (patch).

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

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 <[email protected]>
Reviewed-by: Oleksandr Natalenko <[email protected]>
Acked-by: Bartlomiej Zolnierkiewicz <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

There are 13 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 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 fdd12f8..5c0ca1c 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 786f9aa..a9c69ae 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))

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