diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 9182f84efa9a..dfee0b45a4fc 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1120,6 +1120,24 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 					count = -EINTR;
 					goto out_mm;
 				}
+				/*
+				 * Avoid to modify vma->vm_flags
+				 * without locked ops while the
+				 * coredump reads the vm_flags.
+				 */
+				if (!mmget_still_valid(mm)) {
+					/*
+					 * Silently return "count"
+					 * like if get_task_mm()
+					 * failed. FIXME: should this
+					 * function have returned
+					 * -ESRCH if get_task_mm()
+					 * failed like if
+					 * get_proc_task() fails?
+					 */
+					up_write(&mm->mmap_sem);
+					goto out_mm;
+				}
 				for (vma = mm->mmap; vma; vma = vma->vm_next) {
 					vma->vm_flags &= ~VM_SOFTDIRTY;
 					vma_set_page_prot(vma);
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 9d9c032d5fe5..144d39bf1d48 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -479,6 +479,8 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	 * taking the mmap_sem for writing.
 	 */
 	down_write(&mm->mmap_sem);
+	if (!mmget_still_valid(mm))
+		goto skip_mm;
 	prev = NULL;
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
 		cond_resched();
@@ -502,6 +504,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 		vma->vm_flags = new_flags;
 		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
 	}
+skip_mm:
 	up_write(&mm->mmap_sem);
 	mmput(mm);
 wakeup:
@@ -803,6 +806,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 		goto out;
 
 	down_write(&mm->mmap_sem);
+	if (!mmget_still_valid(mm))
+		goto out_unlock;
+
 	vma = find_vma_prev(mm, start, &prev);
 	if (!vma)
 		goto out_unlock;
@@ -949,6 +955,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 		goto out;
 
 	down_write(&mm->mmap_sem);
+	if (!mmget_still_valid(mm))
+		goto out_unlock;
+
 	vma = find_vma_prev(mm, start, &prev);
 	if (!vma)
 		goto out_unlock;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6038c8a17119..26dd08ff4a77 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1209,6 +1209,26 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long address,
 		unsigned long size, struct zap_details *);
 void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
 		unsigned long start, unsigned long end);
+/*
+ * This has to be called after a get_task_mm()/mmget_not_zero()
+ * followed by taking the mmap_sem for writing before modifying the
+ * vmas or anything the coredump pretends not to change from under it.
+ *
+ * NOTE: find_extend_vma() called from GUP context is the only place
+ * that can modify the "mm" (notably the vm_start/end) under mmap_sem
+ * for reading and outside the context of the process, so it is also
+ * the only case that holds the mmap_sem for reading that must call
+ * this function. Generally if the mmap_sem is hold for reading
+ * there's no need of this check after get_task_mm()/mmget_not_zero().
+ *
+ * This function can be obsoleted and the check can be removed, after
+ * the coredump code will hold the mmap_sem for writing before
+ * invoking the ->core_dump methods.
+ */
+static inline bool mmget_still_valid(struct mm_struct *mm)
+{
+	return likely(!mm->core_state);
+}
 
 /**
  * mm_walk - callbacks for walk_page_range
diff --git a/mm/mmap.c b/mm/mmap.c
index 6441ef827c2d..b41851f32743 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2457,7 +2457,8 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
 	vma = find_vma_prev(mm, addr, &prev);
 	if (vma && (vma->vm_start <= addr))
 		return vma;
-	if (!prev || expand_stack(prev, addr))
+	/* don't alter vm_end if the coredump is running */
+	if (!prev || !mmget_still_valid(mm) || expand_stack(prev, addr))
 		return NULL;
 	if (prev->vm_flags & VM_LOCKED)
 		populate_vma_page_range(prev, addr, prev->vm_end, NULL);
@@ -2483,6 +2484,9 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
 		return vma;
 	if (!(vma->vm_flags & VM_GROWSDOWN))
 		return NULL;
+	/* don't alter vm_start if the coredump is running */
+	if (!mmget_still_valid(mm))
+		return NULL;
 	start = vma->vm_start;
 	if (expand_stack(vma, addr))
 		return NULL;