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vt_ioctl: make VT_RESIZEX behave like VT_RESIZE

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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=32577e96d88447ded2d3b76d71254fb855245837
[2] https://syzkaller.appspot.com/bug?id=6b8355d27b2b94fb5cedf4655e3a59162d9e48e3

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.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tetsuo Handa 2020-09-27 20:46:30 +09:00 committed by Greg Kroah-Hartman
parent b63537020d
commit 988d076336
1 changed files with 10 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
drivers/tty/vt/vt_ioctl.c
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@ -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;
}