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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2020-07-29 16:57:01 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-08-18 13:18:17 +0200
commitf8d1653daec02315e06d30246cff4af72e76e54e (patch)
treea7804e5ed72e52c54f9f0a8c38779919d79952ef /drivers/tty/vt
parentLinux 5.9-rc1 (diff)
downloadlinux-f8d1653daec02315e06d30246cff4af72e76e54e.tar.xz
linux-f8d1653daec02315e06d30246cff4af72e76e54e.zip
vt: defer kfree() of vc_screenbuf in vc_do_resize()
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 Preserving old buffer and tolerating outdated vc members until set_origin() completes would be easier than preventing vc-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con_set_origin() from accessing outdated vc members.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> Cc: stable <stable@vger.kernel.org> Link: https://lore.kernel.org/r/1596034621-4714-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/vt')
-rw-r--r--drivers/tty/vt/vt.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index ccb533fd00a2..a4f08c0da84b 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1201,7 +1201,7 @@ 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();
@@ -1299,10 +1299,11 @@ 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;