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>

4 files changed, 23 insertions, 18 deletions

diff --git a/drivers/input/serio/serport.c b/drivers/input/serio/serport.c
index 8755f5f3ad37..0cb7ef59071b 100644
--- a/drivers/input/serio/serport.c
+++ b/drivers/input/serio/serport.c
@@ -124,7 +124,7 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 {
         struct serport *serport = (struct serport*) tty->disc_data;
         unsigned long flags;
-        unsigned int ch_flags;
+        unsigned int ch_flags = 0;
         int i;
 
         spin_lock_irqsave(&serport->lock, flags);
@@ -133,18 +133,20 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
                 goto out;
 
         for (i = 0; i < count; i++) {
-                switch (fp[i]) {
-                case TTY_FRAME:
-                        ch_flags = SERIO_FRAME;
-                        break;
-
-                case TTY_PARITY:
-                        ch_flags = SERIO_PARITY;
-                        break;
-
-                default:
-                        ch_flags = 0;
-                        break;
+                if (fp) {
+                        switch (fp[i]) {
+                        case TTY_FRAME:
+                                ch_flags = SERIO_FRAME;
+                                break;
+
+                        case TTY_PARITY:
+                                ch_flags = SERIO_PARITY;
+                                break;
+
+                        default:
+                                ch_flags = 0;
+                                break;
+                        }
                 }
 
                 serio_interrupt(serport->serio, cp[i], ch_flags);
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);
diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c
index 1e6405070ce6..8b157d68a03e 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -1244,7 +1244,7 @@ static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 {
         struct r3964_info *pInfo = tty->disc_data;
         const unsigned char *p;
-        char *f, flags = 0;
+        char *f, flags = TTY_NORMAL;
         int i;
 
         for (i = count, p = cp, f = fp; i; i--, p++) {
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index f15c898ff462..b8347c207cb8 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -84,7 +84,8 @@
  *      processing.  <cp> is a pointer to the buffer of input
  *      character received by the device.  <fp> is a pointer to a
  *      pointer of flag bytes which indicate whether a character was
- *      received with a parity error, etc.
+ *      received with a parity error, etc. <fp> may be NULL to indicate
+ *      all data received is TTY_NORMAL.
  *
  * void (*write_wakeup)(struct tty_struct *);
  *
@@ -118,7 +119,8 @@
  *      processing.  <cp> is a pointer to the buffer of input
  *      character received by the device.  <fp> is a pointer to a
  *      pointer of flag bytes which indicate whether a character was
- *      received with a parity error, etc.
+ *      received with a parity error, etc. <fp> may be NULL to indicate
+ *      all data received is TTY_NORMAL.
  *      If assigned, prefer this function for automatic flow control.
  */