The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 988d0763361bb65690d60e2bc53a6b72777040c3 Mon Sep 17 00:00:00 2001

From: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Date: Sun, 27 Sep 2020 20:46:30 +0900 Subject: [PATCH] vt_ioctl: make VT_RESIZEX behave like VT_RESIZE

syzbot is reporting UAF/OOB read at bit_putcs()/soft_cursor() [1][2], for vt_resizex() from ioctl(VT_RESIZEX) allows setting font height larger than actual font height calculated by con_font_set() from ioctl(PIO_FONT). Since fbcon_set_font() from con_font_set() allocates minimal amount of memory based on actual font height calculated by con_font_set(), use of vt_resizex() can cause UAF/OOB read for font data.

VT_RESIZEX was introduced in Linux 1.3.3, but it is unclear that what comes to the "+ more" part, and I couldn't find a user of VT_RESIZEX.

#define VT_RESIZE 0x5609 /* set kernel's idea of screensize */ #define VT_RESIZEX 0x560A /* set kernel's idea of screensize + more */

So far we are not aware of syzbot reports caused by setting non-zero value to v_vlin parameter. But given that it is possible that nobody is using VT_RESIZEX, we can try removing support for v_clin and v_vlin parameters.

Therefore, this patch effectively makes VT_RESIZEX behave like VT_RESIZE, with emitting a message if somebody is still using v_clin and/or v_vlin parameters.

[1] https://syzkaller.appspot.com/bug?id=32577e96d88447ded2d3b76d71254fb85524583... [2] https://syzkaller.appspot.com/bug?id=6b8355d27b2b94fb5cedf4655e3a59162d9e48e...

Reported-by: syzbot syzbot+b308f5fd049fbbc6e74f@syzkaller.appspotmail.com Reported-by: syzbot syzbot+16469b5e8e5a72e9131e@syzkaller.appspotmail.com Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: stable stable@vger.kernel.org Link: https://lore.kernel.org/r/4933b81b-9b1a-355b-df0e-9b31e8280ab9@i-love.sakura... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c index 2ea76a09e07f..0a33b8ababe3 100644 --- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -772,58 +772,21 @@ static int vt_resizex(struct vc_data *vc, struct vt_consize __user *cs) if (copy_from_user(&v, cs, sizeof(struct vt_consize))) return -EFAULT;

- /* FIXME: Should check the copies properly */ - if (!v.v_vlin) - v.v_vlin = vc->vc_scan_lines; - - if (v.v_clin) { - int rows = v.v_vlin / v.v_clin; - if (v.v_rows != rows) { - if (v.v_rows) /* Parameters don't add up */ - return -EINVAL; - v.v_rows = rows; - } - } - - if (v.v_vcol && v.v_ccol) { - int cols = v.v_vcol / v.v_ccol; - if (v.v_cols != cols) { - if (v.v_cols) - return -EINVAL; - v.v_cols = cols; - } - } - - if (v.v_clin > 32) - return -EINVAL; + if (v.v_vlin) + pr_info_once(""struct vt_consize"->v_vlin is ignored. Please report if you need this.\n"); + if (v.v_clin) + pr_info_once(""struct vt_consize"->v_clin is ignored. Please report if you need this.\n");

+ console_lock(); for (i = 0; i < MAX_NR_CONSOLES; i++) { - struct vc_data *vcp; + vc = vc_cons[i].d;

- if (!vc_cons[i].d) - continue; - console_lock(); - vcp = vc_cons[i].d; - if (vcp) { - int ret; - int save_scan_lines = vcp->vc_scan_lines; - int save_font_height = vcp->vc_font.height; - - if (v.v_vlin) - vcp->vc_scan_lines = v.v_vlin; - if (v.v_clin) - vcp->vc_font.height = v.v_clin; - vcp->vc_resize_user = 1; - ret = vc_resize(vcp, v.v_cols, v.v_rows); - if (ret) { - vcp->vc_scan_lines = save_scan_lines; - vcp->vc_font.height = save_font_height; - console_unlock(); - return ret; - } + if (vc) { + vc->vc_resize_user = 1; + vc_resize(vc, v.v_cols, v.v_rows); } - console_unlock(); } + console_unlock();

return 0; }