Security: round mmap hint address above mmap_min_addr

If mmap_min_addr is set and a process attempts to mmap (not fixed) with a
non-null hint address less than mmap_min_addr the mapping will fail the
security checks.  Since this is just a hint address this patch will round
such a hint address above mmap_min_addr.

gcj was found to try to be very frugal with vm usage and give hint addresses
in the 8k-32k range.  Without this patch all such programs failed and with
the patch they happily get a higher address.

This patch is wrappad in CONFIG_SECURITY since mmap_min_addr doesn't exist
without it and there would be no security check possible no matter what.  So
we should not bother compiling in this rounding if it is just a waste of
time.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 520238cbae..1b7b95c67a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -12,6 +12,7 @@
 #include <linux/prio_tree.h>
 #include <linux/debug_locks.h>
 #include <linux/mm_types.h>
+#include <linux/security.h>
 
 struct mempolicy;
 struct anon_vma;
@@ -513,6 +514,21 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
 }
 
 /*
+ * If a hint addr is less than mmap_min_addr change hint to be as
+ * low as possible but still greater than mmap_min_addr
+ */
+static inline unsigned long round_hint_to_min(unsigned long hint)
+{
+#ifdef CONFIG_SECURITY
+        hint &= PAGE_MASK;
+        if (((void *)hint != NULL) &&
+            (hint < mmap_min_addr))
+                return PAGE_ALIGN(mmap_min_addr);
+#endif
+        return hint;
+}
+
+/*
  * Some inline functions in vmstat.h depend on page_zone()
  */
 #include <linux/vmstat.h>