[PATCH] bugfix for drivers/char/mem.c

[Steven Hand <Steven.Hand@cl.cam.ac.uk>]

There is a bug in the function read_kmem() in drivers/char/mem.c  -
the file position is incorrectly updated after a read() from /dev/kmem.
This means that successive reads from /dev/kmem without an intervening
seek will return incorrect data. 

The bug has been around for quite a while, and is present in all the
2.2.x kernels.  The following patch (against v.2.3.12) fixes it.


S.

--- v2.3.12/linux/drivers/char/mem.c	Sun Aug  1 11:09:11 1999
+++ linux/drivers/char/mem.c	Sun Aug  1 11:25:07 1999
@@ -245,11 +245,14 @@
 		count -= read;
 	}
 
-	virtr = vread(buf, (char *)p, count);
-	if (virtr < 0)
-		return virtr;
-	*ppos += p + virtr;
-	return virtr + read;
+	if(count) {
+		if((virtr = vread(buf, (char *)p, count)) < 0)
+			return virtr;
+		read += virtr;
+	}
+
+	*ppos += read;
+	return read;
 }
 
 /*


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