fbdev: fbcon: Properly revert changes when vc_resize() failed

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
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+

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 4a032fc..098b62f 100644 (file)
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2401,15 +2401,21 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
        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;
@@ -2425,7 +2431,9 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
                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);
@@ -2435,6 +2443,21 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
        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;
 }
 
 /*