The patch titled Subject: userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails has been added to the -mm tree. Its filename is userfaultfd-remove-uffd-flags-from-vma-vm_flags-if-uffd_event_fork-fails.patch
This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-remove-uffd-flags-from-... and later at http://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-remove-uffd-flags-from-...
Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated there every 3-4 working days
------------------------------------------------------ From: Mike Rapoport rppt@linux.vnet.ibm.com 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@linux.vnet.i... Fixes: 0cbb4b4f4c44 ("userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails") 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 Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
diff -puN fs/userfaultfd.c~userfaultfd-remove-uffd-flags-from-vma-vm_flags-if-uffd_event_fork-fails fs/userfaultfd.c --- 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); _
Patches currently in -mm which might be from rppt@linux.vnet.ibm.com are
userfaultfd-remove-uffd-flags-from-vma-vm_flags-if-uffd_event_fork-fails.patch mm-make-deferred_struct_page_init-explicitly-depend-on-sparsemem.patch mm-memblock-replace-u64-with-phys_addr_t-where-appropriate.patch mm-mempool-add-missing-parameter-description.patch mm-util-make-strndup_user-description-a-kernel-doc-comment.patch mm-util-add-kernel-doc-for-kvfree.patch docs-core-api-kill-trailing-whitespace-in-kernel-apirst.patch docs-core-api-move-strmemdup-to-string-manipulation.patch docs-core-api-split-memory-management-api-to-a-separate-file.patch docs-mm-make-gfp-flags-descriptions-usable-as-kernel-doc.patch docs-core-api-mm-api-add-section-about-gfp-flags.patch