| From: Peter Xu <peterx@redhat.com> |
| Subject: Revert "userfaultfd: don't fail on unrecognized features" |
| Date: Wed, 12 Apr 2023 12:38:52 -0400 |
| |
| This is a proposal to revert commit 914eedcb9ba0ff53c33808. |
| |
| I found this when writing a simple UFFDIO_API test to be the first unit |
| test in this set. Two things breaks with the commit: |
| |
| - UFFDIO_API check was lost and missing. According to man page, the |
| kernel should reject ioctl(UFFDIO_API) if uffdio_api.api != 0xaa. This |
| check is needed if the api version will be extended in the future, or |
| user app won't be able to identify which is a new kernel. |
| |
| - Feature flags checks were removed, which means UFFDIO_API with a |
| feature that does not exist will also succeed. According to the man |
| page, we should (and it makes sense) to reject ioctl(UFFDIO_API) if |
| unknown features passed in. |
| |
| Link: https://lore.kernel.org/r/20220722201513.1624158-1-axelrasmussen@google.com |
| Link: https://lkml.kernel.org/r/20230412163922.327282-2-peterx@redhat.com |
| Fixes: 914eedcb9ba0 ("userfaultfd: don't fail on unrecognized features") |
| Signed-off-by: Peter Xu <peterx@redhat.com> |
| Acked-by: David Hildenbrand <david@redhat.com> |
| Cc: Axel Rasmussen <axelrasmussen@google.com> |
| Cc: Dmitry Safonov <0x7f454c46@gmail.com> |
| Cc: Mike Kravetz <mike.kravetz@oracle.com> |
| Cc: Mike Rapoport (IBM) <rppt@kernel.org> |
| Cc: Zach O'Keefe <zokeefe@google.com> |
| Cc: <stable@vger.kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| fs/userfaultfd.c | 6 ++++-- |
| 1 file changed, 4 insertions(+), 2 deletions(-) |
| |
| --- a/fs/userfaultfd.c~revert-userfaultfd-dont-fail-on-unrecognized-features |
| +++ a/fs/userfaultfd.c |
| @@ -1955,8 +1955,10 @@ static int userfaultfd_api(struct userfa |
| ret = -EFAULT; |
| if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) |
| goto out; |
| - /* Ignore unsupported features (userspace built against newer kernel) */ |
| - features = uffdio_api.features & UFFD_API_FEATURES; |
| + features = uffdio_api.features; |
| + ret = -EINVAL; |
| + if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) |
| + goto err_out; |
| ret = -EPERM; |
| if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE)) |
| goto err_out; |
| _ |
