mmap: 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 <[email protected]>

---

 include/linux/mm.h |   16 ++++++++++++++++
 mm/mmap.c          |    3 +++
 mm/nommu.c         |    3 +++
 3 files changed, 22 insertions(+), 0 deletions(-)

include/linux/mm.h +16 -0

index 520238c..1b7b95c 100644
@@ -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>

mm/mmap.c +3 -0

index 938313c..f4cfc6a 100644
@@ -912,6 +912,9 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
 	if (!len)
 		return -EINVAL;
 
+	if (!(flags & MAP_FIXED))
+		addr = round_hint_to_min(addr);
+
 	error = arch_mmap_check(addr, len, flags);
 	if (error)
 		return error;

mm/nommu.c +3 -0

index 35622c5..b989cb9 100644
@@ -829,6 +829,9 @@ unsigned long do_mmap_pgoff(struct file *file,
 	void *result;
 	int ret;
 
+	if (!(flags & MAP_FIXED))
+		addr = round_hint_to_min(addr);
+
 	/* decide whether we should attempt the mapping, and if so what sort of
 	 * mapping */
 	ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,