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authorJiri Slaby <jslaby@suse.cz>2020-10-19 10:55:17 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-10-28 13:41:02 +0100
commit82e61c3909db51d91b9d3e2071557b6435018b80 (patch)
tree6bab8c7be70bedb5c5799ae702573d10d6e4dff0 /drivers/tty/vt
parent6ca03f90527e499dd5e32d6522909e2ad390896b (diff)
vt: keyboard, extend func_buf_lock to readers
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/vt')
-rw-r--r--drivers/tty/vt/keyboard.c17
1 files changed, 13 insertions, 4 deletions
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 7bfa95c3252c..78acc270e39a 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -743,8 +743,13 @@ 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);
}
@@ -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 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;
}