linux-kernel - Re: [syzbot] [crypto?] KASAN: slab-use-after-free Read in handle_mm

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Message-Id: <20240716115504.1136-1-hdanton@sina.com>
Date: Tue, 16 Jul 2024 19:55:04 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+4c882a4a0697c4a25364@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [crypto?] KASAN: slab-use-after-free Read in handle_mm_fault

On Tue, 16 Jul 2024 01:29:17 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    3fe121b62282 Add linux-next specific files for 20240712
> git tree:       linux-next
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13ce3259980000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  3fe121b62282

--- x/mm/memory.c
+++ y/mm/memory.c
@@ -5808,6 +5808,7 @@ vm_fault_t handle_mm_fault(struct vm_are
 	/* If the fault handler drops the mmap_lock, vma may be freed */
 	struct mm_struct *mm = vma->vm_mm;
 	vm_fault_t ret;
+	bool droppable;
 
 	__set_current_state(TASK_RUNNING);
 
@@ -5831,6 +5832,7 @@ vm_fault_t handle_mm_fault(struct vm_are
 
 	lru_gen_enter_fault(vma);
 
+	droppable = !!(vma->vm_flags & VM_DROPPABLE);
 	if (unlikely(is_vm_hugetlb_page(vma)))
 		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
 	else
@@ -5839,7 +5841,7 @@ vm_fault_t handle_mm_fault(struct vm_are
 	lru_gen_exit_fault();
 
 	/* If the mapping is droppable, then errors due to OOM aren't fatal. */
-	if (vma->vm_flags & VM_DROPPABLE)
+	if (droppable)
 		ret &= ~VM_FAULT_OOM;
 
 	if (flags & FAULT_FLAG_USER) {
--