On 2020/09/27 4:39, Peilin Ye wrote:
On Sun, Sep 27, 2020 at 01:25:17AM +0900, Tetsuo Handa wrote:
Since I don't know the meaning of "struct vt_consize"->v_clin (which is commented with "/* number of pixel rows per character */" but does it mean font size ?), I don't know why we can assign that value to vcp->vc_font.height via
if (v.v_clin) vcp->vc_font.height = v.v_clin;
in vt_resizex(). While ioctl(PIO_FONT) needs to pass vc->vc_sw->con_font_set() check in con_font_set(), ioctl(VT_RESIZEX) does not pass it in vt_resizex()...
Since this problem does not happen if I remove
if (v.v_clin) vcp->vc_font.height = v.v_clin;
Hi Tetsuo!
from vt_resizex(), I guess that some variables are getting confused by change of vc->vc_font.height ...
Yes, see bit_putcs():
(drivers/video/fbdev/core/bitblit.c) static void bit_putcs(struct vc_data *vc, struct fb_info *info, const unsigned short *s, int count, int yy, int xx, int fg, int bg) { struct fb_image image; u32 width = DIV_ROUND_UP(vc->vc_font.width, 8); u32 cellsize = width * vc->vc_font.height; ^^^^^^^^ ^^^^^^^^^^^^^^
`cellsize` is now too large. Later, in bit_putcs_aligned():
while (cnt--) { src = vc->vc_font.data + (scr_readw(s++)& charmask)*cellsize; ^^^^^^^^
`src` goes out of bounds of the data buffer. At first glance I guess this is an out-of-bound read reported as a use-after-free read? The crashlog says:
How this OOB access is reported varies.
To resolve this out-of-bound issue for now, I think the easiest way is to add a range check in bit_putcs(), or bit_putcs_aligned().
...but yeah, that `VT_RESIZEX` ioctl looks really buggy, and is already causing more issues:
At least, since not all fonts have height == 32 (e.g. font_vga_8x8 is height == 8), allow changing vc->vc_font.height with only
if (v.v_clin > 32) return -EINVAL;
validation in VT_RESIZEX looks wrong. This needs more validations.
By the way, can we find a user of VT_RESIZEX? As far as I googled with "VT_RESIZEX", I couldn't find a userspace program; only explanation of VT_RESIZEX and kernel patches related to VT_RESIZEX are found. Also, while console_ioctl(4) man page says
Any parameter may be set to zero, indicating "no change"
, the assignment
if (!v.v_vlin) v.v_vlin = vc->vc_scan_lines;
changes the meaning to
If v_vlin parameter is set to zero, the value for associated console is copied to each console (instead of preserving current value for that console)
. Maybe for now we can try this (effectively making VT_RESIZEX == VT_RESIZE) ?
vt_ioctl.c | 57 ++++++++++----------------------------------------------- 1 file changed, 10 insertions(+), 47 deletions(-)
diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c index a4e520bdd521..bc33938e2f20 100644 --- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -773,58 +773,21 @@ 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; }