vm: fix vm_pgoff wrap in stack expansion

BugLink: http://bugs.launchpad.net/bugs/769042

commit a626ca6a656450e9f4df91d0dda238fff23285f4 upstream.

Commit 982134ba6261 ("mm: avoid wrapping vm_pgoff in mremap()") fixed
the case of a expanding mapping causing vm_pgoff wrapping when you used
mremap.  But there was another case where we expand mappings hiding in
plain sight: the automatic stack expansion.

This fixes that case too.

This one also found by Robert Święcki, using his nasty system call
fuzzer tool.  Good job.

Reported-and-tested-by: Robert Święcki <robert@swiecki.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>

diff --git a/mm/mmap.c b/mm/mmap.c
index d908a25..8b25d31 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1914,11 +1914,14 @@ static int expand_downwards(struct vm_area_struct *vma,
                size = vma->vm_end - address;
                grow = (vma->vm_start - address) >> PAGE_SHIFT;
 
-               error = acct_stack_growth(vma, size, grow);
-               if (!error) {
-                       vma->vm_start = address;
-                       vma->vm_pgoff -= grow;
-                       perf_event_mmap(vma);
+               error = -ENOMEM;
+               if (grow <= vma->vm_pgoff) {
+                       error = acct_stack_growth(vma, size, grow);
+                       if (!error) {
+                               vma->vm_start = address;
+                               vma->vm_pgoff -= grow;
+                               perf_event_mmap(vma);
+                       }
                }
        }
        vma_unlock_anon_vma(vma);