[Qemu-devel] [PATCH 1/7] userfaultfd: require UFFDIO_API before other ioctls

[Andrea Arcangeli]

UFFDIO_API was already forced before read/poll could work. This
makes the code more strict to force it also for all other ioctls.

All users would already have been required to call UFFDIO_API before
invoking other ioctls but this makes it more explicit.

This will ensure we can change all ioctls (all but UFFDIO_API/struct
uffdio_api) with a bump of uffdio_api.api.

There's no actual plan or need to change the API or the ioctl, the
current API already should cover fine even the non cooperative usage,
but this is just for the longer term future just in case.

Signed-off-by: Andrea Arcangeli <address@hidden>
---
 fs/userfaultfd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 5f11678..b69d236 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1115,6 +1115,12 @@ static long userfaultfd_ioctl(struct file *file, 
unsigned cmd,
        int ret = -EINVAL;
        struct userfaultfd_ctx *ctx = file->private_data;
 
+       if (cmd != UFFDIO_API) {
+               if (ctx->state == UFFD_STATE_WAIT_API)
+                       return -EINVAL;
+               BUG_ON(ctx->state != UFFD_STATE_RUNNING);
+       }
+
        switch(cmd) {
        case UFFDIO_API:
                ret = userfaultfd_api(ctx, arg);