[CRIU] [PATCH 3/4] remap: add a dead pid /proc remap

[Pavel Emelyanov]

I've pushed the changes, looked at them and found 2 bugs :)

> @@ -516,6 +550,20 @@ static int dump_linked_remap(char *path, int len, const struct stat *ost,
>  			&rpe, PB_REMAP_FPATH);
>  }
>  
> +static int dump_dead_process_remap(pid_t pid, char *path, int len, const struct stat *ost,
> +				int lfd, u32 id, struct ns_id *nsid)
> +{
> +	RemapFilePathEntry rpe = REMAP_FILE_PATH_ENTRY__INIT;
> +
> +	rpe.orig_id = id;
> +	rpe.remap_id = pid;
> +	rpe.has_remap_type = true;
> +	rpe.remap_type = REMAP_TYPE__PROCFS;

This code would produce duplicate entries if equal dead pids are 
opened by more than one file.

> +
> +	return pb_write_one(fdset_fd(glob_fdset, CR_FD_REMAP_FPATH),
> +			&rpe, PB_REMAP_FPATH);
> +}
> +
>  static bool is_sillyrename_name(char *name)
>  {
>  	int i;
> @@ -557,6 +605,38 @@ static int check_path_remap(char *rpath, int plen, const struct fd_parms *parms,
>  	struct stat pst;
>  	const struct stat *ost = &parms->stat;
>  
> +	if (parms->fs_type == PROC_SUPER_MAGIC) {
> +		/* The file points to /proc/pid/<foo> where pid is a dead
> +		 * process. We remap this file by adding this pid to be
> +		 * fork()ed into a TASK_HELPER state so that we can point to it
> +		 * on restore.
> +		 */
> +		pid_t pid;
> +		char *start, *end;
> +
> +		/* skip "./proc/" */
> +		start = strstr(rpath, "/") + 1;
> +		if (!start)
> +			return -1;
> +		start = strstr(start, "/") + 1;
> +		if (!start)
> +			return -1;
> +		pid = strtol(start, &end, 10);
> +
> +		/* if we didn't find another /, this path something
> +		 * like ./proc/kmsg, which we shouldn't mess with. */
> +		if (*end == '/') {
> +			*end = 0;
> +			ret = access(rpath, F_OK);
> +			*end = '/';
> +
> +			if (ret) {
> +				pr_info("Dumping dead process remap of %d\n", pid);
> +				return dump_dead_process_remap(pid, rpath + 1, plen - 1, ost, lfd, id, nsid);
> +			}
> +		}

On these else branches we would go and execute the rest of the
remap code, while we shouldn't.

> +	}
> +
>  	if (ost->st_nlink == 0)
>  		/*
>  		 * Unpleasant, but easy case. File is completely invisible