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From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Sun, 10 May 2015 12:45:21 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r282725 - head/sys/dev/usb/video
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Author: hselasky
Date: Sun May 10 12:45:21 2015
New Revision: 282725
URL: https://svnweb.freebsd.org/changeset/base/282725

Log:
  Put recycle pointer in own memory area which is not mmap'able.

Modified:
  head/sys/dev/usb/video/udl.c

Modified: head/sys/dev/usb/video/udl.c
==============================================================================
--- head/sys/dev/usb/video/udl.c	Sun May 10 12:41:34 2015	(r282724)
+++ head/sys/dev/usb/video/udl.c	Sun May 10 12:45:21 2015	(r282725)
@@ -203,12 +203,14 @@ udl_buffer_alloc(uint32_t size)
 	}
 	mtx_unlock(&udl_buffer_mtx);
 	if (buf != NULL) {
+		uint8_t *ptr = ((uint8_t *)buf) - size;
 		/* wipe and recycle buffer */
-		memset(buf, 0, size);
-		return (buf);
+		memset(ptr, 0, size);
+		/* return buffer pointer */
+		return (ptr);
 	}
 	/* allocate new buffer */
-	return (malloc(size, M_USB_DL, M_WAITOK | M_ZERO));
+	return (malloc(size + sizeof(*buf), M_USB_DL, M_WAITOK | M_ZERO));
 }
 
 static void
@@ -216,9 +218,11 @@ udl_buffer_free(void *_buf, uint32_t siz
 {
 	struct udl_buffer *buf;
 
-	buf = (struct udl_buffer *)_buf;
-	if (buf == NULL)
+	/* check for NULL pointer */
+	if (_buf == NULL)
 		return;
+	/* compute pointer to recycle list */
+	buf = (struct udl_buffer *)(((uint8_t *)_buf) + size);
 
 	/*
 	 * Memory mapped buffers should never be freed.