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Commit 130c03c8 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Greg Kroah-Hartman
Browse files

vt: defer kfree() of vc_screenbuf in vc_do_resize() 

commit f8d1653daec02315e06d30246cff4af72e76e54e upstream.

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Preserving old buffer and tolerating outdated vc members until set_origin()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accessing outdated vc members.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: default avatarsyzbot <syzbot+9116ecc1978ca3a12f43@syzkaller.appspotmail.com>
Signed-off-by: default avatarTetsuo 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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e35d476b

drivers/tty/vt/vt.c

+3 −2
Original line number Diff line number Diff line
@@ -864,7 +864,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc, 
	unsigned int old_rows, old_row_size;

	unsigned int new_cols, new_rows, new_row_size, new_screen_size;

	unsigned int user;

	unsigned short *newscreen;

	unsigned short *oldscreen, *newscreen;



	WARN_CONSOLE_UNLOCKED();
@@ -946,10 +946,11 @@ 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;