Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

Cross-merge networking fixes after downstream PR.

No conflicts or adjacent changes.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 16 insertions, 12 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 01f39e8144ef..603b2f419948 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5393,27 +5393,28 @@ retry:
 	if (!vma_is_anonymous(vma) && !vma_is_tcp(vma))
 		goto inval;
 
-	/* find_mergeable_anon_vma uses adjacent vmas which are not locked */
-	if (!vma->anon_vma && !vma_is_tcp(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 && !vma_is_tcp(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) {
@@ -5425,6 +5426,9 @@ retry:
 
 	rcu_read_unlock();
 	return vma;
+
+inval_end_read:
+	vma_end_read(vma);
 inval:
 	rcu_read_unlock();
 	count_vm_vma_lock_event(VMA_LOCK_ABORT);