Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7e3ba72e authored by Jiri Slaby's avatar Jiri Slaby Committed by Greg Kroah-Hartman
Browse files

vt: keyboard, extend func_buf_lock to readers 



commit 82e61c3909db51d91b9d3e2071557b6435018b80 upstream.

Both read-side users of func_table/func_buf need locking. Without that,
one can easily confuse the code by repeatedly setting altering strings
like:
while (1)
	for (a = 0; a < 2; a++) {
		struct kbsentry kbs = {};
		strcpy((char *)kbs.kb_string, a ? ".\n" : "88888\n");
		ioctl(fd, KDSKBSENT, &kbs);
	}

When that program runs, one can get unexpected output by holding F1
(note the unxpected period on the last line):
.
88888
.8888

So protect all accesses to 'func_table' (and func_buf) by preexisting
'func_buf_lock'.

It is easy in 'k_fn' handler as 'puts_queue' is expected not to sleep.
On the other hand, KDGKBSENT needs a local (atomic) copy of the string
because copy_to_user can sleep. Use already allocated, but unused
'kbs->kb_string' for that purpose.

Note that the program above needs at least CAP_SYS_TTY_CONFIG.

This depends on the previous patch and on the func_buf_lock lock added
in commit 46ca3f735f34 (tty/vt: fix write/write race in ioctl(KDSKBSENT)
handler) in 5.2.

Likely fixes CVE-2020-25656.

Cc: <stable@vger.kernel.org>
Reported-by: default avatarMinh Yuan <yuanmingbuaa@gmail.com>
Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20201019085517.10176-2-jslaby@suse.cz


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 20cf3fcd

drivers/tty/vt/keyboard.c

+13 −4
Original line number Original line Diff line number Diff line
@@ -742,8 +742,13 @@ static void k_fn(struct vc_data *vc, unsigned char value, char up_flag) 
		return;

		return;





	if ((unsigned)value < ARRAY_SIZE(func_table)) {

	if ((unsigned)value < ARRAY_SIZE(func_table)) {

		unsigned long flags;



		spin_lock_irqsave(&func_buf_lock, flags);

		if (func_table[value])

		if (func_table[value])

			puts_queue(vc, func_table[value]);

			puts_queue(vc, func_table[value]);

		spin_unlock_irqrestore(&func_buf_lock, flags);



	} else

	} else

		pr_err("k_fn called with value=%d\n", value);

		pr_err("k_fn called with value=%d\n", value);

}

}
@@ -1990,7 +1995,7 @@ int vt_do_kdsk_ioctl(int cmd, struct kbentry __user *user_kbe, int perm, 
#undef s

#undef s

#undef v

#undef v





/* FIXME: This one needs untangling and locking */

/* FIXME: This one needs untangling */

int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)

int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)

{

{

	struct kbsentry *kbs;

	struct kbsentry *kbs;
@@ -2022,10 +2027,14 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm) 
	switch (cmd) {

	switch (cmd) {

	case KDGKBSENT: {

	case KDGKBSENT: {

		/* size should have been a struct member */

		/* size should have been a struct member */

		unsigned char *from = func_table[i] ? : "";

		ssize_t len = sizeof(user_kdgkb->kb_string);



		spin_lock_irqsave(&func_buf_lock, flags);

		len = strlcpy(kbs->kb_string, func_table[i] ? : "", len);

		spin_unlock_irqrestore(&func_buf_lock, flags);





		ret = copy_to_user(user_kdgkb->kb_string, from,

		ret = copy_to_user(user_kdgkb->kb_string, kbs->kb_string,

				strlen(from) + 1) ? -EFAULT : 0;

				len + 1) ? -EFAULT : 0;





		goto reterr;

		goto reterr;

	}

	}