[PATCH 4.9 81/92] tty: wipe buffer if not echoing data

Greg Kroah-Hartman
2018-11-29T14:23:40Z

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 | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -154,17 +154,28 @@ static inline unsigned char *echo_buf_ad
return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
}

+/* If we are not echoing the data, perhaps this is a secret so erase it */
+static 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 int tty_copy_to_user(struct tty_struct *tty, void __user *to,
size_t tail, size_t n)
{
struct n_tty_data *ldata = tty->disc_data;
size_t size = N_TTY_BUF_SIZE - tail;
- const void *from = read_buf_addr(ldata, tail);
+ void *from = read_buf_addr(ldata, tail);
int uncopied;

if (n > size) {
tty_audit_add_data(tty, from, size);
uncopied = copy_to_user(to, from, size);
+ zero_buffer(tty, from, size - uncopied);
if (uncopied)
return uncopied;
to += size;
@@ -173,7 +184,9 @@ static int tty_copy_to_user(struct tty_s
}

tty_audit_add_data(tty, from, n);
- return copy_to_user(to, from, n);
+ uncopied = copy_to_user(to, from, n);
+ zero_buffer(tty, from, n - uncopied);
+ return uncopied;
}

/**
@@ -1962,11 +1975,12 @@ static int copy_from_read_buf(struct tty
n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
n = min(*nr, n);
if (n) {
- const unsigned char *from = read_buf_addr(ldata, tail);
+ unsigned char *from = read_buf_addr(ldata, tail);
retval = copy_to_user(*b, from, n);
n -= retval;
is_eof = n == 1 && *from == EOF_CHAR(tty);
tty_audit_add_data(tty, from, n);
+ zero_buffer(tty, from, 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 &&