1 files changed, 50 insertions, 23 deletions

diff --git a/drivers/staging/android/logger.c b/drivers/staging/android/logger.c
index ffc2d043dd8..0d2367f2c15 100644
--- a/drivers/staging/android/logger.c
+++ b/drivers/staging/android/logger.c
@@ -60,7 +60,11 @@ struct logger_reader {
 };
 
 /* logger_offset - returns index 'n' into the log via (optimized) modulus */
-#define logger_offset(n)	((n) & (log->size - 1))
+size_t logger_offset(struct logger_log *log, size_t n)
+{
+	return n & (log->size-1);
+}
+
 
 /*
  * file_get_log - Given a file structure, return the associated log
@@ -89,20 +93,24 @@ static inline struct logger_log *file_get_log(struct file *file)
  * get_entry_len - Grabs the length of the payload of the next entry starting
  * from 'off'.
  *
+ * An entry length is 2 bytes (16 bits) in host endian order.
+ * In the log, the length does not include the size of the log entry structure.
+ * This function returns the size including the log entry structure.
+ *
  * Caller needs to hold log->mutex.
  */
 static __u32 get_entry_len(struct logger_log *log, size_t off)
 {
 	__u16 val;
 
-	switch (log->size - off) {
-	case 1:
-		memcpy(&val, log->buffer + off, 1);
-		memcpy(((char *) &val) + 1, log->buffer, 1);
-		break;
-	default:
-		memcpy(&val, log->buffer + off, 2);
-	}
+	/* copy 2 bytes from buffer, in memcpy order, */
+	/* handling possible wrap at end of buffer */
+
+	((__u8 *)&val)[0] = log->buffer[off];
+	if (likely(off+1 < log->size))
+		((__u8 *)&val)[1] = log->buffer[off+1];
+	else
+		((__u8 *)&val)[1] = log->buffer[0];
 
 	return sizeof(struct logger_entry) + val;
 }
@@ -137,7 +145,7 @@ static ssize_t do_read_log_to_user(struct logger_log *log,
 		if (copy_to_user(buf + len, log->buffer, count - len))
 			return -EFAULT;
 
-	reader->r_off = logger_offset(reader->r_off + count);
+	reader->r_off = logger_offset(log, reader->r_off + count);
 
 	return count;
 }
@@ -164,9 +172,10 @@ static ssize_t logger_read(struct file *file, char __user *buf,
 
 start:
 	while (1) {
+		mutex_lock(&log->mutex);
+
 		prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
 
-		mutex_lock(&log->mutex);
 		ret = (log->w_off == reader->r_off);
 		mutex_unlock(&log->mutex);
 		if (!ret)
@@ -225,7 +234,7 @@ static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
 
 	do {
 		size_t nr = get_entry_len(log, off);
-		off = logger_offset(off + nr);
+		off = logger_offset(log, off + nr);
 		count += nr;
 	} while (count < len);
 
@@ -233,16 +242,28 @@ static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
 }
 
 /*
- * clock_interval - is a < c < b in mod-space? Put another way, does the line
- * from a to b cross c?
+ * is_between - is a < c < b, accounting for wrapping of a, b, and c
+ *    positions in the buffer
+ *
+ * That is, if a<b, check for c between a and b
+ * and if a>b, check for c outside (not between) a and b
+ *
+ * |------- a xxxxxxxx b --------|
+ *               c^
+ *
+ * |xxxxx b --------- a xxxxxxxxx|
+ *    c^
+ *  or                    c^
  */
-static inline int clock_interval(size_t a, size_t b, size_t c)
+static inline int is_between(size_t a, size_t b, size_t c)
 {
-	if (b < a) {
-		if (a < c || b >= c)
+	if (a < b) {
+		/* is c between a and b? */
+		if (a < c && c <= b)
 			return 1;
 	} else {
-		if (a < c && b >= c)
+		/* is c outside of b through a? */
+		if (c <= b || a < c)
 			return 1;
 	}
 
@@ -260,14 +281,14 @@ static inline int clock_interval(size_t a, size_t b, size_t c)
 static void fix_up_readers(struct logger_log *log, size_t len)
 {
 	size_t old = log->w_off;
-	size_t new = logger_offset(old + len);
+	size_t new = logger_offset(log, old + len);
 	struct logger_reader *reader;
 
-	if (clock_interval(old, new, log->head))
+	if (is_between(old, new, log->head))
 		log->head = get_next_entry(log, log->head, len);
 
 	list_for_each_entry(reader, &log->readers, list)
-		if (clock_interval(old, new, reader->r_off))
+		if (is_between(old, new, reader->r_off))
 			reader->r_off = get_next_entry(log, reader->r_off, len);
 }
 
@@ -286,7 +307,7 @@ static void do_write_log(struct logger_log *log, const void *buf, size_t count)
 	if (count != len)
 		memcpy(log->buffer, buf + len, count - len);
 
-	log->w_off = logger_offset(log->w_off + count);
+	log->w_off = logger_offset(log, log->w_off + count);
 
 }
 
@@ -309,9 +330,15 @@ static ssize_t do_write_log_from_user(struct logger_log *log,
 
 	if (count != len)
 		if (copy_from_user(log->buffer, buf + len, count - len))
+			/*
+			 * Note that by not updating w_off, this abandons the
+			 * portion of the new entry that *was* successfully
+			 * copied, just above.  This is intentional to avoid
+			 * message corruption from missing fragments.
+			 */
 			return -EFAULT;
 
-	log->w_off = logger_offset(log->w_off + count);
+	log->w_off = logger_offset(log, log->w_off + count);
 
 	return count;
 }