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Subject[PATCH v5 23/25] userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally
Date
Only declare _UFFDIO_WRITEPROTECT if the user specified
UFFDIO_REGISTER_MODE_WP and if all the checks passed. Then when the
user registers regions with shmem/hugetlbfs we won't expose the new
ioctl to them. Even with complete anonymous memory range, we'll only
expose the new WP ioctl bit if the register mode has MODE_WP.

Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
fs/userfaultfd.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 498971fa9163..4e1d7748224a 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1465,14 +1465,24 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
up_write(&mm->mmap_sem);
mmput(mm);
if (!ret) {
+ __u64 ioctls_out;
+
+ ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
+ UFFD_API_RANGE_IOCTLS;
+
+ /*
+ * Declare the WP ioctl only if the WP mode is
+ * specified and all checks passed with the range
+ */
+ if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
+ ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
+
/*
* Now that we scanned all vmas we can already tell
* userland which ioctls methods are guaranteed to
* succeed on this range.
*/
- if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
- UFFD_API_RANGE_IOCTLS,
- &user_uffdio_register->ioctls))
+ if (put_user(ioctls_out, &user_uffdio_register->ioctls))
ret = -EFAULT;
}
out:
--
2.21.0
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