lkml.org 
[lkml]   [2020]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] vt: defer kfree() of vc_screenbuf in vc_do_resize()
Date
syzbot is reporting UAF bug in set_origin() from vc_do_resize() [1], for
vc_do_resize() calls kfree(vc->vc_screenbuf) before calling set_origin().

Unfortunately, in set_origin(), vc->vc_sw->con_set_origin() might access
vc->vc_pos when scroll is involved in order to manipulate cursor, but
vc->vc_pos refers already released vc->vc_screenbuf until vc->vc_pos gets
updated based on the result of vc->vc_sw->con_set_origin().

Preserving old buffer and tolerating outdated vc members until set_origin()
completes would be easier than preventing vc->vc_sw->con_set_origin() from
accessing outdated vc members.

[1] https://syzkaller.appspot.com/bug?id=6649da2081e2ebdc65c0642c214b27fe91099db3

Reported-by: syzbot <syzbot+9116ecc1978ca3a12f43@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
drivers/tty/vt/vt.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 42d8c67..c9ee8e9 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1196,7 +1196,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
unsigned int old_rows, old_row_size, first_copied_row;
unsigned int new_cols, new_rows, new_row_size, new_screen_size;
unsigned int user;
- unsigned short *newscreen;
+ unsigned short *oldscreen, *newscreen;
struct uni_screen *new_uniscr = NULL;

WARN_CONSOLE_UNLOCKED();
@@ -1294,10 +1294,11 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
if (new_scr_end > new_origin)
scr_memsetw((void *)new_origin, vc->vc_video_erase_char,
new_scr_end - new_origin);
- kfree(vc->vc_screenbuf);
+ oldscreen = vc->vc_screenbuf;
vc->vc_screenbuf = newscreen;
vc->vc_screenbuf_size = new_screen_size;
set_origin(vc);
+ kfree(oldscreen);

/* do part of a reset_terminal() */
vc->vc_top = 0;
--
1.8.3.1
\
 
 \ /
  Last update: 2020-07-29 16:58    [W:0.043 / U:0.468 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site