| From 82e61c3909db51d91b9d3e2071557b6435018b80 Mon Sep 17 00:00:00 2001 |
| From: Jiri Slaby <jirislaby@kernel.org> |
| Date: Mon, 19 Oct 2020 10:55:17 +0200 |
| Subject: vt: keyboard, extend func_buf_lock to readers |
| |
| From: Jiri Slaby <jslaby@suse.cz> |
| |
| 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: Minh Yuan <yuanmingbuaa@gmail.com> |
| Signed-off-by: Jiri Slaby <jslaby@suse.cz> |
| Link: https://lore.kernel.org/r/20201019085517.10176-2-jslaby@suse.cz |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/tty/vt/keyboard.c | 17 +++++++++++++---- |
| 1 file changed, 13 insertions(+), 4 deletions(-) |
| |
| --- a/drivers/tty/vt/keyboard.c |
| +++ b/drivers/tty/vt/keyboard.c |
| @@ -743,8 +743,13 @@ static void k_fn(struct vc_data *vc, uns |
| return; |
| |
| if ((unsigned)value < ARRAY_SIZE(func_table)) { |
| + unsigned long flags; |
| + |
| + spin_lock_irqsave(&func_buf_lock, flags); |
| if (func_table[value]) |
| puts_queue(vc, func_table[value]); |
| + spin_unlock_irqrestore(&func_buf_lock, flags); |
| + |
| } else |
| pr_err("k_fn called with value=%d\n", value); |
| } |
| @@ -1991,7 +1996,7 @@ out: |
| #undef s |
| #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) |
| { |
| struct kbsentry *kbs; |
| @@ -2023,10 +2028,14 @@ int vt_do_kdgkb_ioctl(int cmd, struct kb |
| switch (cmd) { |
| case KDGKBSENT: { |
| /* 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, |
| - strlen(from) + 1) ? -EFAULT : 0; |
| + ret = copy_to_user(user_kdgkb->kb_string, kbs->kb_string, |
| + len + 1) ? -EFAULT : 0; |
| |
| goto reterr; |
| } |