[PATCH 5.19 121/158] fbdev: fbcon: Properly revert changes when vc_resize() failed

Greg Kroah-Hartman
2022-08-29T11:35:13Z

From: Shigeru Yoshida <syoshida@redhat.com>

commit a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24 upstream.

fbcon_do_set_font() calls vc_resize() when font size is changed.
However, if if vc_resize() failed, current implementation doesn't
revert changes for font size, and this causes inconsistent state.

syzbot reported unable to handle page fault due to this issue [1].
syzbot's repro uses fault injection which cause failure for memory
allocation, so vc_resize() failed.

This patch fixes this issue by properly revert changes for font
related date when vc_resize() failed.

Link: https://syzkaller.appspot.com/bug?id=3443d3a1fa6d964dd7310a0cb1696d165a3e07c4 [1]
Reported-by: syzbot+a168dbeaaa7778273c1b@syzkaller.appspotmail.com
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Signed-off-by: Helge Deller <deller@gmx.de>
CC: stable@vger.kernel.org # 5.15+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/video/fbdev/core/fbcon.c | 27 +++++++++++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2402,15 +2402,21 @@ static int fbcon_do_set_font(struct vc_d
struct fb_info *info = fbcon_info_from_console(vc->vc_num);
struct fbcon_ops *ops = info->fbcon_par;
struct fbcon_display *p = &fb_display[vc->vc_num];
- int resize;
+ int resize, ret, old_userfont, old_width, old_height, old_charcount;
char *old_data = NULL;

resize = (w != vc->vc_font.width) || (h != vc->vc_font.height);
if (p->userfont)
old_data = vc->vc_font.data;
vc->vc_font.data = (void *)(p->fontdata = data);
+ old_userfont = p->userfont;
if ((p->userfont = userfont))
REFCOUNT(data)++;
+
+ old_width = vc->vc_font.width;
+ old_height = vc->vc_font.height;
+ old_charcount = vc->vc_font.charcount;
+
vc->vc_font.width = w;
vc->vc_font.height = h;
vc->vc_font.charcount = charcount;
@@ -2426,7 +2432,9 @@ static int fbcon_do_set_font(struct vc_d
rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
cols /= w;
rows /= h;
- vc_resize(vc, cols, rows);
+ ret = vc_resize(vc, cols, rows);
+ if (ret)
+ goto err_out;
} else if (con_is_visible(vc)
&& vc->vc_mode == KD_TEXT) {
fbcon_clear_margins(vc, 0);
@@ -2436,6 +2444,21 @@ static int fbcon_do_set_font(struct vc_d
if (old_data && (--REFCOUNT(old_data) == 0))
kfree(old_data - FONT_EXTRA_WORDS * sizeof(int));
return 0;
+
+err_out:
+ p->fontdata = old_data;
+ vc->vc_font.data = (void *)old_data;
+
+ if (userfont) {
+ p->userfont = old_userfont;
+ REFCOUNT(data)--;
+ }
+
+ vc->vc_font.width = old_width;
+ vc->vc_font.height = old_height;
+ vc->vc_font.charcount = old_charcount;
+
+ return ret;
}

/*