Messages in this thread Patch in this message | | | Date | Wed, 18 Jul 2018 10:12:31 +0300 | From | Mike Rapoport <> | Subject | Re: kernel BUG at fs/userfaultfd.c:LINE! (2) |
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On Tue, Jul 17, 2018 at 12:28:06PM -0700, Eric Biggers wrote: > [+Cc userfaultfd developers and linux-mm] > > The reproducer hits the BUG_ON() in userfaultfd_release(): > > BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ > !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
Thanks for the CC.
The fix is below.
-- Sincerely yours, Mike.
From 3711b6a72abe3796b2b97fdba8eadd995b29f195 Mon Sep 17 00:00:00 2001 From: Mike Rapoport <rppt@linux.vnet.ibm.com> Date: Wed, 18 Jul 2018 09:45:54 +0300 Subject: [PATCH] userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails
The fix in commit 0cbb4b4f4c44 ("userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails") cleared the vma->vm_userfaultfd_ctx but kept userfaultfd flags in vma->vm_flags that were copied from the parent process VMA.
As the result, there is an inconsistency between the values of vma->vm_userfaultfd_ctx.ctx and vma->vm_flags which triggers BUG_ON in userfaultfd_release().
Clearing the uffd flags from vma->vm_flags in case of UFFD_EVENT_FORK failure resolves the issue.
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reported-by: syzbot+121be635a7a35ddb7dcb@syzkaller.appspotmail.com Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Eric Biggers <ebiggers3@gmail.com> Cc: stable@vger.kernel.org --- fs/userfaultfd.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 594d192b2331..bad9cea37f12 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -633,8 +633,10 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, /* the various vma->vm_userfaultfd_ctx still points to it */ down_write(&mm->mmap_sem); for (vma = mm->mmap; vma; vma = vma->vm_next) - if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) + if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) { vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING); + } up_write(&mm->mmap_sem); userfaultfd_ctx_put(release_new_ctx); -- 2.7.4
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