Hi Al,
Could you please review/apply this patch?
Thanks,
Miklos
On Thu, Nov 28, 2019 at 4:59 PM Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
>
> Avi Kivity reports that on fuse filesystems running in a user namespace
> asyncronous fsync fails with EOVERFLOW.
>
> The reason is that f_ops->fsync() is called with the creds of the kthread
> performing aio work instead of the creds of the process originally
> submitting IOCB_CMD_FSYNC.
>
> Fuse sends the creds of the caller in the request header and it needs to
> translate the uid and gid into the server's user namespace. Since the
> kthread is running in init_user_ns, the translation will fail and the
> operation returns an error.
>
> It can be argued that fsync doesn't actually need any creds, but just
> zeroing out those fields in the header (as with requests that currently
> don't take creds) is a backward compatibility risk.
>
> Instead of working around this issue in fuse, solve the core of the problem
> by calling the filesystem with the proper creds.
>
> Reported-by: Avi Kivity <avi@xxxxxxxxxxxx>
> Tested-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
> Fixes: c9582eb0ff7d ("fuse: Fail all requests with invalid uids or gids")
> Cc: stable@xxxxxxxxxxxxxxx # 4.18+
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
> fs/aio.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 0d9a559d488c..37828773e2fe 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -176,6 +176,7 @@ struct fsync_iocb {
> struct file *file;
> struct work_struct work;
> bool datasync;
> + struct cred *creds;
> };
>
> struct poll_iocb {
> @@ -1589,8 +1590,11 @@ static int aio_write(struct kiocb *req, const struct iocb *iocb,
> static void aio_fsync_work(struct work_struct *work)
> {
> struct aio_kiocb *iocb = container_of(work, struct aio_kiocb, fsync.work);
> + const struct cred *old_cred = override_creds(iocb->fsync.creds);
>
> iocb->ki_res.res = vfs_fsync(iocb->fsync.file, iocb->fsync.datasync);
> + revert_creds(old_cred);
> + put_cred(iocb->fsync.creds);
> iocb_put(iocb);
> }
>
> @@ -1604,6 +1608,10 @@ static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
> if (unlikely(!req->file->f_op->fsync))
> return -EINVAL;
>
> + req->creds = prepare_creds();
> + if (!req->creds)
> + return -ENOMEM;
> +
> req->datasync = datasync;
> INIT_WORK(&req->work, aio_fsync_work);
> schedule_work(&req->work);
> --
> 2.21.0
>
