* [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx
[not found] <d4583416-5e4a-95e7-a08a-32bf2c9a95fb@huawei.com>
@ 2019-08-20 16:02 ` Oleg Nesterov
2019-08-20 16:05 ` Andrea Arcangeli
2019-08-21 0:53 ` Kefeng Wang
0 siblings, 2 replies; 3+ messages in thread
From: Oleg Nesterov @ 2019-08-20 16:02 UTC (permalink / raw)
To: Kefeng Wang
Cc: linux-mm, Andrea Arcangeli, Peter Xu, Mike Rapoport, Jann Horn,
Jason Gunthorpe, Michal Hocko, Andrew Morton, Tetsuo Handa,
linux-kernel
userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even
if mm->core_state != NULL.
Otherwise a page fault can see userfaultfd_missing() == T and use an
already freed userfaultfd_ctx.
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Fixes: 04f5866e41fb ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping")
Cc: stable@vger.kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/userfaultfd.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ccbdbd6..fe6d804 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -880,6 +880,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
/* len == 0 means wake all */
struct userfaultfd_wake_range range = { .len = 0, };
unsigned long new_flags;
+ bool still_valid;
WRITE_ONCE(ctx->released, true);
@@ -895,8 +896,7 @@ 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;
+ still_valid = mmget_still_valid(mm);
prev = NULL;
for (vma = mm->mmap; vma; vma = vma->vm_next) {
cond_resched();
@@ -907,19 +907,20 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
continue;
}
new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
- prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
- new_flags, vma->anon_vma,
- vma->vm_file, vma->vm_pgoff,
- vma_policy(vma),
- NULL_VM_UFFD_CTX);
- if (prev)
- vma = prev;
- else
- prev = vma;
+ if (still_valid) {
+ prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
+ new_flags, vma->anon_vma,
+ vma->vm_file, vma->vm_pgoff,
+ vma_policy(vma),
+ NULL_VM_UFFD_CTX);
+ if (prev)
+ vma = prev;
+ else
+ prev = vma;
+ }
vma->vm_flags = new_flags;
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
}
-skip_mm:
up_write(&mm->mmap_sem);
mmput(mm);
wakeup:
--
2.5.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx
2019-08-20 16:02 ` [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx Oleg Nesterov
@ 2019-08-20 16:05 ` Andrea Arcangeli
2019-08-21 0:53 ` Kefeng Wang
1 sibling, 0 replies; 3+ messages in thread
From: Andrea Arcangeli @ 2019-08-20 16:05 UTC (permalink / raw)
To: Oleg Nesterov
Cc: Kefeng Wang, linux-mm, Peter Xu, Mike Rapoport, Jann Horn,
Jason Gunthorpe, Michal Hocko, Andrew Morton, Tetsuo Handa,
linux-kernel
On Tue, Aug 20, 2019 at 06:02:38PM +0200, Oleg Nesterov wrote:
> userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even
> if mm->core_state != NULL.
>
> Otherwise a page fault can see userfaultfd_missing() == T and use an
> already freed userfaultfd_ctx.
>
> Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Fixes: 04f5866e41fb ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping")
> Cc: stable@vger.kernel.org
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> fs/userfaultfd.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Thanks,
Andrea
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx
2019-08-20 16:02 ` [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx Oleg Nesterov
2019-08-20 16:05 ` Andrea Arcangeli
@ 2019-08-21 0:53 ` Kefeng Wang
1 sibling, 0 replies; 3+ messages in thread
From: Kefeng Wang @ 2019-08-21 0:53 UTC (permalink / raw)
To: Oleg Nesterov
Cc: linux-mm, Andrea Arcangeli, Peter Xu, Mike Rapoport, Jann Horn,
Jason Gunthorpe, Michal Hocko, Andrew Morton, Tetsuo Handa,
linux-kernel
On 2019/8/21 0:02, Oleg Nesterov wrote:
> userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even
> if mm->core_state != NULL.
>
> Otherwise a page fault can see userfaultfd_missing() == T and use an
> already freed userfaultfd_ctx.
>
> Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Fixes: 04f5866e41fb ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping")
> Cc: stable@vger.kernel.org
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> fs/userfaultfd.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
Tested on lts4.4 and 5.3-rc4, Thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-08-20 16:02 ` [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx Oleg Nesterov
2019-08-20 16:05 ` Andrea Arcangeli
2019-08-21 0:53 ` Kefeng Wang
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