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| author | Jiri Slaby <jslaby@suse.cz> | 2020-10-19 10:55:17 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-11-10 10:23:58 +0100 |
| commit | 04a6e5aa75e7a9432df0443a17ab7c8dd005cc9b (patch) | |
| tree | 7bfbeac0cd583b09eb690005af4ef6989675eb62 /drivers/tty | |
| parent | 2f7ed3b41f24ea9a083e73b715e1e0277d8d14bb (diff) | |
| download | linux-stable-04a6e5aa75e7a9432df0443a17ab7c8dd005cc9b.tar.gz linux-stable-04a6e5aa75e7a9432df0443a17ab7c8dd005cc9b.tar.bz2 linux-stable-04a6e5aa75e7a9432df0443a17ab7c8dd005cc9b.zip | |
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: 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>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/vt/keyboard.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c index bb90df4975bb..4bc6261ef3c1 100644 --- a/drivers/tty/vt/keyboard.c +++ b/drivers/tty/vt/keyboard.c @@ -712,8 +712,13 @@ static void k_fn(struct vc_data *vc, unsigned char value, char up_flag) 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); } @@ -1959,7 +1964,7 @@ 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; @@ -1991,10 +1996,14 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm) 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; } |