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    Subject[PATCH] fbcon: Properly revert changes when vc_resize() failed
    Date
    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>
    ---
    drivers/video/fbdev/core/fbcon.c | 27 +++++++++++++++++++++++++--
    1 file changed, 25 insertions(+), 2 deletions(-)

    diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
    index cf9ac4da0a82..825b012debe7 100644
    --- 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;
    }

    /*
    --
    2.37.1
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