On 08/03/2010 07:11 PM, Sukadev Bhattiprolu wrote:
> Restore the file-owner information for each 'struct file'. This is
> essentially is like a new fcntl(F_SETOWN) and fcntl(F_SETSIG) calls,
> except that the pid, uid, euid and signum values are read from the
> checkpoint image.
>
> Changelog[v3]:
> - [Oren Laadan]: Ensure find_vpid() found a valid pid before
> making it the file owner.
> Changelog[v2]:
> - [Matt Helsley, Serge Hallyn]: Don't trust uids in checkpoint image.
> (added CAP_KILL check)
> - Check that signal number read from the checkpoint image is valid.
> (not sure it is required, since its an incomplete check for tampering)
>
> Signed-off-by: Sukadev Bhattiprolu<[email protected]>
I may have missed a previous discussion on this - but: do you
plan to relate the uid/euid to the userns ?
[...]
> diff --git a/fs/checkpoint.c b/fs/checkpoint.c
> index ce1b4af..b5486c1 100644
> --- a/fs/checkpoint.c
> +++ b/fs/checkpoint.c
> @@ -618,6 +618,68 @@ static int attach_file(struct file *file)
> return fd;
> }
>
> +static int restore_file_owner(struct ckpt_ctx *ctx, struct ckpt_hdr_file *h,
> + struct file *file)
> +{
> + int ret;
> + struct pid *pid;
> + uid_t uid, euid;
> +
> + uid = h->f_owner_uid;
> + euid = h->f_owner_euid;
> +
> + ckpt_debug("restore_file_owner(): uid %u, euid %u, pid %d, type %d\n",
> + uid, euid, h->f_owner_pid, h->f_owner_pid_type);
> + /*
> + * We can't trust the uids in the checkpoint image and normally need
> + * CAP_KILL. But if the uids match our ids, should be fine since we
> + * have access to the file.
> + *
> + * TODO: Move this check to __f_setown() ?
> + */
> + ret = -EACCES;
> + if (!capable(CAP_KILL)&&
> + (uid != current_uid() || euid != current_euid())) {
> + ckpt_err(ctx, ret, "image uids [%d, %d] don't match current "
> + "process uids [%d, %d] and no CAP_KILL\n",
> + uid, euid, current_uid(), current_euid());
> + return ret;
> + }
> +
> + ret = -EINVAL;
> + if (!valid_signal(h->f_owner_signum)) {
> + ckpt_err(ctx, ret, "Invalid signum %d\n", h->f_owner_signum);
> + return ret;
> + }
> + file->f_owner.signum = h->f_owner_signum;
> +
> + rcu_read_lock();
> +
> + /*
> + * If file had a non-NULL owner and we can't find the owner after
> + * restart, return error.
> + */
> + pid = find_vpid(h->f_owner_pid);
> + if (h->f_owner_pid&& !pid)
> + ret = -ESRCH;
> + else {
> + /*
> + * TODO: Do we need 'force' to be 1 here or can it be 0 ?
> + * 'force' is used to modify the owner, if one is
> + * already set. Can it be set when we restart an
> + * application ?
> + */
> + ret = __f_setown(file, pid, h->f_owner_pid_type, uid, euid, 1);
__f_setown() does not check its pid_type argument - you need
to sanitize here, no ?
(and not that I expect the PIDTYPE_... will ever change, but -
possibly encode the PIDTYPE_... types into CKPT_PIDTYPE_... )
[...]
Oren.
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