[PATCH 5/6] fsx: Add check for mmap last-page zero fill

["Theodore Ts'o" <tytso@xxxxxxx>]

Check to make sure the VM system provided 0's beyond the true end of
the file mapping (as required by mmap def in 1996 posix 1003.1)

This check was taken from the FreeBSD version of fsx.c.

Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
---
 ltp/fsx.c |   35 +++++++++++++++++++++++++++++++++++
 1 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/ltp/fsx.c b/ltp/fsx.c
index d1d1ed8..2ef9c0f 100644
--- a/ltp/fsx.c
+++ b/ltp/fsx.c
@@ -9,6 +9,8 @@
  *     Rewritten 8/98 by Conrad Minshall.
  *
  *     Small changes to work under Linux -- davej.
+ *
+ *     Checks for mmap last-page zero fill.
  */
 
 #include "global.h"
@@ -504,6 +506,33 @@ doread(unsigned offset, unsigned size)
 
 
 void
+check_eofpage(char *s, unsigned offset, char *p, int size)
+{
+       unsigned long last_page, should_be_zero;
+
+       if (offset + size <= (file_size & ~page_mask))
+               return;
+       /*
+        * we landed in the last page of the file
+        * test to make sure the VM system provided 0's 
+        * beyond the true end of the file mapping
+        * (as required by mmap def in 1996 posix 1003.1)
+        */
+       last_page = ((unsigned long)p + (offset & page_mask) + size) & 
~page_mask;
+
+       for (should_be_zero = last_page + (file_size & page_mask);
+            should_be_zero < last_page + page_size;
+            should_be_zero++)
+               if (*(char *)should_be_zero) {
+                       prt("Mapped %s: non-zero data past EOF (0x%llx) page 
offset 0x%x is 0x%04x\n",
+                           s, file_size - 1, should_be_zero & page_mask,
+                           short_at(should_be_zero));
+                       report_failure(205);
+               }
+}
+
+
+void
 domapread(unsigned offset, unsigned size)
 {
        unsigned pg_offset;
@@ -547,6 +576,9 @@ domapread(unsigned offset, unsigned size)
                report_failure(190);
        }
        memcpy(temp_buf, p + pg_offset, size);
+
+       check_eofpage("Read", offset, p, size);
+
        if (munmap(p, map_size) != 0) {
                prterr("domapread: munmap");
                report_failure(191);
@@ -696,6 +728,9 @@ domapwrite(unsigned offset, unsigned size)
                prterr("domapwrite: msync");
                report_failure(203);
        }
+
+       check_eofpage("Write", offset, p, size);
+
        if (munmap(p, map_size) != 0) {
                prterr("domapwrite: munmap");
                report_failure(204);
-- 
1.6.3.rc4.1.g3e14.dirty