mm/fremap.c: fix oops on error path

If find_vma() fails, sys_remap_file_pages() will dereference `vma', which
contains NULL.  Fix it by checking the pointer.

(We could alternatively check for err==0, but this seems more direct)

(The vm_flags change is to squish a bogus used-uninitialised warning
without adding extra code).

Reported-by: Tommi Rantala <tt.rantala@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 0cd4c11488ed..6a8da7ee85fd 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -163,7 +163,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
          * and that the remapped range is valid and fully within
          * the single existing vma.
          */
-        if (!vma || !(vma->vm_flags & VM_SHARED))
+        vm_flags = vma->vm_flags;
+        if (!vma || !(vm_flags & VM_SHARED))
                 goto out;
 
         if (!vma->vm_ops || !vma->vm_ops->remap_pages)
@@ -254,7 +255,8 @@ get_write_lock:
          */
 
 out:
-        vm_flags = vma->vm_flags;
+        if (vma)
+                vm_flags = vma->vm_flags;
         if (likely(!has_write_lock))
                 up_read(&mm->mmap_sem);
         else