[PATCH 4.4 80/86] tty: wipe buffer if not echoing data

Greg Kroah-Hartman
2018-11-29T14:20:33Z

From: Greg Kroah-Hartman <greg@kroah.com>

commit b97b3d9fb57860a60592859e332de7759fd54c2e upstream.

If we are not echoing the data to userspace or the console is in icanon
mode, then perhaps it is a "secret" so we should wipe it once we are
done with it.

This mirrors the logic that the audit code has.

Reported-by: aszlig <aszlig@nix.build>
Tested-by: Milan Broz <gmazyland@gmail.com>
Tested-by: Daniel Zatovic <daniel.zatovic@gmail.com>
Tested-by: aszlig <aszlig@nix.build>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/tty/n_tty.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -165,15 +165,29 @@ static inline int tty_put_user(struct tt
return put_user(x, ptr);
}

+/* If we are not echoing the data, perhaps this is a secret so erase it */
+static inline void zero_buffer(struct tty_struct *tty, u8 *buffer, int size)
+{
+ bool icanon = !!L_ICANON(tty);
+ bool no_echo = !L_ECHO(tty);
+
+ if (icanon && no_echo)
+ memset(buffer, 0x00, size);
+}
+
static inline int tty_copy_to_user(struct tty_struct *tty,
void __user *to,
- const void *from,
+ void *from,
unsigned long n)
{
struct n_tty_data *ldata = tty->disc_data;
+ int retval;

tty_audit_add_data(tty, from, n, ldata->icanon);
- return copy_to_user(to, from, n);
+ retval = copy_to_user(to, from, n);
+ if (!retval)
+ zero_buffer(tty, from, n);
+ return retval;
}

/**
@@ -2005,6 +2019,7 @@ static int copy_from_read_buf(struct tty
is_eof = n == 1 && read_buf(ldata, tail) == EOF_CHAR(tty);
tty_audit_add_data(tty, read_buf_addr(ldata, tail), n,
ldata->icanon);
+ zero_buffer(tty, read_buf_addr(ldata, tail), n);
smp_store_release(&ldata->read_tail, ldata->read_tail + n);
/* Turn single EOF into zero-length read */
if (L_EXTPROC(tty) && ldata->icanon && is_eof &&