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Preserving old buffer and tolerating outdated vc members until set_origin() completes would be easier than preventing vc-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con_set_origin() from accessing outdated vc members.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=6649da2081e2ebdc65c0642c214b27fe91099db...
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;
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Preserving old buffer and tolerating outdated vc members until set_origin() completes would be easier than preventing vc-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=6649da2081e2ebdc65c0642c214b27fe91099db...
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;
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=6649da2081e2ebdc65c0642c214b27fe91099db...
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;
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
On 2020/08/04 21:58, Greg Kroah-Hartman wrote:
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() ?
I think what you have here is fine, as cleaning up set_orgin() might be hard to do at this point in time.
Seems that there is no comment. Greg, will you pick up this patch?
On Wed, Aug 12, 2020 at 12:02:03AM +0900, Tetsuo Handa wrote:
On 2020/08/04 21:58, Greg Kroah-Hartman wrote:
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() ?
I think what you have here is fine, as cleaning up set_orgin() might be hard to do at this point in time.
Seems that there is no comment. Greg, will you pick up this patch?
Yes, will do after -rc1 is out.
thanks,
greg k-h
dri-devel@lists.freedesktop.org
-
Greg Kroah-Hartman -
Tetsuo Handa -
Tetsuo Handa