bas_gigaset: collapse CR/LF at end of AT response

Copy the mechanism from ser_/usb_gigaset to avoid producing
spurious empty responses for CR/LF sequences from the device.
Add a comment in all drivers documenting that behaviour.
Correct an off by one error that might result in a one byte
buffer overflow when receiving an unexpectedly long reply.

Impact: minor bugfix
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 35 insertions, 15 deletions

diff --git a/drivers/isdn/gigaset/asyncdata.c b/drivers/isdn/gigaset/asyncdata.c
index ccb2a7b7c41d..e913beb63f24 100644
--- a/drivers/isdn/gigaset/asyncdata.c
+++ b/drivers/isdn/gigaset/asyncdata.c
@@ -40,6 +40,8 @@ static inline int muststuff(unsigned char c)
  * Append received bytes to the command response buffer and forward them
  * line by line to the response handler. Exit whenever a mode/state change
  * might have occurred.
+ * Note: Received lines may be terminated by CR, LF, or CR LF, which will be
+ * removed before passing the line to the response handler.
  * Return value:
  *      number of processed bytes
  */
diff --git a/drivers/isdn/gigaset/gigaset.h b/drivers/isdn/gigaset/gigaset.h
index e963a6c2e86d..c9ccf7de2275 100644
--- a/drivers/isdn/gigaset/gigaset.h
+++ b/drivers/isdn/gigaset/gigaset.h
@@ -38,7 +38,7 @@
 #define GIG_COMPAT  {0, 4, 0, 0}
 
 #define MAX_REC_PARAMS 10       /* Max. number of params in response string */
-#define MAX_RESP_SIZE 512       /* Max. size of a response string */
+#define MAX_RESP_SIZE 511       /* Max. size of a response string */
 
 #define MAX_EVENTS 64           /* size of event queue */
 
@@ -498,7 +498,7 @@ struct cardstate {
         spinlock_t ev_lock;
 
         /* current modem response */
-        unsigned char respdata[MAX_RESP_SIZE];
+        unsigned char respdata[MAX_RESP_SIZE+1];
         unsigned cbytes;
 
         /* private data of hardware drivers */
diff --git a/drivers/isdn/gigaset/isocdata.c b/drivers/isdn/gigaset/isocdata.c
index 85394a6ebae8..16fd3bd48883 100644
--- a/drivers/isdn/gigaset/isocdata.c
+++ b/drivers/isdn/gigaset/isocdata.c
@@ -905,29 +905,49 @@ void gigaset_isoc_receive(unsigned char *src, unsigned count,
 
 /* == data input =========================================================== */
 
+/* process a block of received bytes in command mode (mstate != MS_LOCKED)
+ * Append received bytes to the command response buffer and forward them
+ * line by line to the response handler.
+ * Note: Received lines may be terminated by CR, LF, or CR LF, which will be
+ * removed before passing the line to the response handler.
+ */
 static void cmd_loop(unsigned char *src, int numbytes, struct inbuf_t *inbuf)
 {
         struct cardstate *cs = inbuf->cs;
         unsigned cbytes      = cs->cbytes;
+        unsigned char c;
 
         while (numbytes--) {
-                /* copy next character, check for end of line */
-                switch (cs->respdata[cbytes] = *src++) {
-                case '\r':
+                c = *src++;
+                switch (c) {
                 case '\n':
-                        /* end of line */
-                        gig_dbg(DEBUG_TRANSCMD, "%s: End of Command (%d Bytes)",
-                                __func__, cbytes);
-                        if (cbytes >= MAX_RESP_SIZE - 1)
-                                dev_warn(cs->dev, "response too large\n");
+                        if (cbytes == 0 && cs->respdata[0] == '\r') {
+                                /* collapse LF with preceding CR */
+                                cs->respdata[0] = 0;
+                                break;
+                        }
+                        /* --v-- fall through --v-- */
+                case '\r':
+                        /* end of message line, pass to response handler */
+                        if (cbytes >= MAX_RESP_SIZE) {
+                                dev_warn(cs->dev, "response too large (%d)\n",
+                                         cbytes);
+                                cbytes = MAX_RESP_SIZE;
+                        }
                         cs->cbytes = cbytes;
+                        gigaset_dbg_buffer(DEBUG_TRANSCMD, "received response",
+                                           cbytes, cs->respdata);
                         gigaset_handle_modem_response(cs);
                         cbytes = 0;
+
+                        /* store EOL byte for CRLF collapsing */
+                        cs->respdata[0] = c;
                         break;
                 default:
-                        /* advance in line buffer, checking for overflow */
-                        if (cbytes < MAX_RESP_SIZE - 1)
-                                cbytes++;
+                        /* append to line buffer if possible */
+                        if (cbytes < MAX_RESP_SIZE)
+                                cs->respdata[cbytes] = c;
+                        cbytes++;
                 }
         }
 
@@ -958,8 +978,6 @@ void gigaset_isoc_input(struct inbuf_t *inbuf)
                                            numbytes, src);
                         gigaset_if_receive(inbuf->cs, src, numbytes);
                 } else {
-                        gigaset_dbg_buffer(DEBUG_CMD, "received response",
-                                           numbytes, src);
                         cmd_loop(src, numbytes, inbuf);
                 }