tty: wipe buffer if not echoing data

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>

1 files changed, 17 insertions, 3 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 431742201709..3ad460219fd6 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -152,17 +152,28 @@ static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
         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;
@@ -171,7 +182,9 @@ static int tty_copy_to_user(struct tty_struct *tty, void __user *to,
         }
 
         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;
 }
 
 /**
@@ -1960,11 +1973,12 @@ static int copy_from_read_buf(struct tty_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 &&