On Tue, Aug 04, 2020 at 08:15:43PM +0900, Tetsuo Handa wrote: > Do you think this approach is acceptable? Or, do we need to modify set_origin() ? > > On 2020/07/29 23:57, Tetsuo Handa wrote: > > 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 Preserving old buffer and tolerating outdated vc members until set_origin() 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 accessing outdated vc members.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@xxxxxxxxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > > --- > > 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; I think what you have here is fine, as cleaning up set_orgin() might be hard to do at this point in time. thanks, greg k-h _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
