From: Suren Baghdasaryan surenb@google.com
commit 33313a747e81af9f31d0d45de78c9397fa3655eb upstream.
mmap_region adds a newly created VMA into VMA tree and might modify it afterwards before dropping the mmap_lock. This poses a problem for page faults handled under per-VMA locks because they don't take the mmap_lock and can stumble on this VMA while it's still being modified. Currently this does not pose a problem since post-addition modifications are done only for file-backed VMAs, which are not handled under per-VMA lock. However, once support for handling file-backed page faults with per-VMA locks is added, this will become a race.
Fix this by write-locking the VMA before inserting it into the VMA tree. Other places where a new VMA is added into VMA tree do not modify it after the insertion, so do not need the same locking.
Cc: stable@vger.kernel.org Signed-off-by: Suren Baghdasaryan surenb@google.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/mmap.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/mm/mmap.c +++ b/mm/mmap.c @@ -2804,6 +2804,8 @@ cannot_expand: if (vma->vm_file) i_mmap_lock_write(vma->vm_file->f_mapping);
+ /* Lock the VMA since it is modified after insertion into VMA tree */ + vma_start_write(vma); vma_iter_store(&vmi, vma); mm->map_count++; if (vma->vm_file) {