On Mon, 31 Jul 2023 at 23:28, <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> The patch below does not apply to the 6.4-stable tree.
Ahh. The vma_is_tcp() checks are new.
I think you can literally just remove all occurrences of
&& !vma_is_tcp(vma)
in that patch to make it apply.
The end result should look something like the attached, afaik.
Linus
diff --git a/mm/memory.c b/mm/memory.c
index f69fbc251198..addf57a42785 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5284,27 +5284,28 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
if (!vma_is_anonymous(vma))
goto inval;
- /* find_mergeable_anon_vma uses adjacent vmas which are not locked */
- if (!vma->anon_vma)
- goto inval;
-
if (!vma_start_read(vma))
goto inval;
+ /*
+ * find_mergeable_anon_vma uses adjacent vmas which are not locked.
+ * This check must happen after vma_start_read(); otherwise, a
+ * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
+ * from its anon_vma.
+ */
+ if (unlikely(!vma->anon_vma))
+ goto inval_end_read;
+
/*
* Due to the possibility of userfault handler dropping mmap_lock, avoid
* it for now and fall back to page fault handling under mmap_lock.
*/
- if (userfaultfd_armed(vma)) {
- vma_end_read(vma);
- goto inval;
- }
+ if (userfaultfd_armed(vma))
+ goto inval_end_read;
/* Check since vm_start/vm_end might change before we lock the VMA */
- if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
- vma_end_read(vma);
- goto inval;
- }
+ if (unlikely(address < vma->vm_start || address >= vma->vm_end))
+ goto inval_end_read;
/* Check if the VMA got isolated after we found it */
if (vma->detached) {
@@ -5316,6 +5317,9 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
rcu_read_unlock();
return vma;
+
+inval_end_read:
+ vma_end_read(vma);
inval:
rcu_read_unlock();
count_vm_vma_lock_event(VMA_LOCK_ABORT);
