From: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Subject: userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails
The fix in 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.
Link: http://lkml.kernel.org/r/1532931975-25473-1-git-send-email-rppt@xxxxxxxxxxxxxxxxxx
Fixes: 0cbb4b4f4c44 ("userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails")
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Reported-by: syzbot+121be635a7a35ddb7dcb@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Eric Biggers <ebiggers3@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/fs/userfaultfd.c~userfaultfd-remove-uffd-flags-from-vma-vm_flags-if-uffd_event_fork-fails
+++ a/fs/userfaultfd.c
@@ -633,8 +633,10 @@ static void userfaultfd_event_wait_compl
/* 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);
_
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