tty: Always handle NULL flag ptr

Most line disciplines already handle the undocumented NULL flag
ptr in their .receive_buf method; however, several don't.

Document the NULL flag ptr, and correct handling in the
N_MOUSE, N_GSM0710 and N_R394 line disciplines.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c0f76da55304..c09db11b8831 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2269,14 +2269,15 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
         char *f;
         int i;
         char buf[64];
-        char flags;
+        char flags = TTY_NORMAL;
 
         if (debug & 4)
                 print_hex_dump_bytes("gsmld_receive: ", DUMP_PREFIX_OFFSET,
                                      cp, count);
 
         for (i = count, dp = cp, f = fp; i; i--, dp++) {
-                flags = *f++;
+                if (f)
+                        flags = *f++;
                 switch (flags) {
                 case TTY_NORMAL:
                         gsm->receive(gsm, *dp);