VM/Security: add security hook to do_brk

Given a specifically crafted binary do_brk() can be used to get low pages
available in userspace virtual memory and can thus be used to circumvent
the mmap_min_addr low memory protection.  Add security checks in do_brk().

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Alan Cox <alan@redhat.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index facc1a75bd4f..acfc13f23ca0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1934,6 +1934,10 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
         if (is_hugepage_only_range(mm, addr, len))
                 return -EINVAL;
 
+        error = security_file_mmap(0, 0, 0, 0, addr, 1);
+        if (error)
+                return error;
+
         flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
 
         error = arch_mmap_check(addr, len, flags);