vm: fix vm_pgoff wrap in stack expansion

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>
[PG: .34 doesn't have perf call via 3af9e859 (in .36); adjust accordingly]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/mm/mmap.c b/mm/mmap.c
index b42b4693fb4fe54d8272ae111352058cb99af30e..fe9b76ae4238b6daeb2f7b9a5430f0c691a77e7d 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1784,10 +1784,13 @@ 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;
+               error = -ENOMEM;
+               if (grow <= vma->vm_pgoff) {
+                       error = acct_stack_growth(vma, size, grow);
+                       if (!error) {
+                               vma->vm_start = address;
+                               vma->vm_pgoff -= grow;
+                       }
                }
        }
        anon_vma_unlock(vma);