[CRIU] [PATCH v3 26/33] utils: Introduce open_fd_of_real_pid()

[Kirill Tkhai]

On 21.02.2017 10:36, Andrei Vagin wrote:
> On Thu, Feb 16, 2017 at 03:10:24PM +0300, Kirill Tkhai wrote:
>> As access to /proc/[pid]/fd/[i] of a task from parent's
>> user_ns is prohibited, introduce a helper, doing that
>> via usernsd.
> 
> Could you explain where are you going to use it?

In "[PATCH v3 29/33] shmem: Fixup shmem_wait_and_open() opens foreign /proc/[pid]/fd/[i]"

>>
>> Also, remove BUG_ON() in usernsd, as now it may be used
>> without input fd parameter.
>>
>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>> ---
>>  criu/include/util.h |    2 ++
>>  criu/namespaces.c   |    5 -----
>>  criu/util.c         |   30 ++++++++++++++++++++++++++++++
>>  3 files changed, 32 insertions(+), 5 deletions(-)
>>
>> diff --git a/criu/include/util.h b/criu/include/util.h
>> index d9f50f6e0..c1d38c939 100644
>> --- a/criu/include/util.h
>> +++ b/criu/include/util.h
>> @@ -307,4 +307,6 @@ extern int epoll_del_rfd(int epfd, struct epoll_rfd *rfd);
>>  extern int epoll_run_rfds(int epfd, struct epoll_event *evs, int nr_fds, int tmo);
>>  extern int epoll_prepare(int nr_events, struct epoll_event **evs);
>>  
>> +extern int open_fd_of_real_pid(pid_t pid, int fd, int flags);
>> +
>>  #endif /* __CR_UTIL_H__ */
>> diff --git a/criu/namespaces.c b/criu/namespaces.c
>> index 518b0af4e..bf4c16d08 100644
>> --- a/criu/namespaces.c
>> +++ b/criu/namespaces.c
>> @@ -1447,11 +1447,6 @@ static int usernsd(int sk)
>>  		unsc_msg_pid_fd(&um, &pid, &fd);
>>  		pr_debug("uns: daemon calls %p (%d, %d, %x)\n", call, pid, fd, flags);
>>  
>> -		if (fd < 0 && flags & UNS_FDOUT) {
>> -			pr_err("uns: bad flags/fd %p %d %x\n", call, fd, flags);
>> -			BUG();
>> -		}
>> -
>>  		/*
>>  		 * Caller has sent us bare address of the routine it
>>  		 * wants to call. Since the caller is fork()-ed from the
>> diff --git a/criu/util.c b/criu/util.c
>> index 6e36b2654..51adcd3d7 100644
>> --- a/criu/util.c
>> +++ b/criu/util.c
>> @@ -1315,3 +1315,33 @@ int epoll_prepare(int nr_fds, struct epoll_event **events)
>>  	xfree(*events);
>>  	return -1;
>>  }
>> +
>> +static int fn_open_proc_r(void *path, int fd, pid_t pid)
>> +{
>> +	return openat(get_service_fd(CR_PROC_FD_OFF), path, O_RDONLY);
>> +}
>> +static int fn_open_proc_w(void *path, int fd, pid_t pid)
>> +{
>> +	return openat(get_service_fd(CR_PROC_FD_OFF), path, O_WRONLY);
>> +}
>> +static int fn_open_proc_rw(void *path, int fd, pid_t pid)
>> +{
>> +	return openat(get_service_fd(CR_PROC_FD_OFF), path, O_RDWR);
>> +}
>> +
>> +int open_fd_of_real_pid(pid_t pid, int fd, int flags)
>> +{
>> +	char path[64];
>> +	int ret;
>> +
>> +	ret = sprintf(path, "%d/fd/%d", pid, fd);
>> +	if (flags == O_RDONLY)
>> +		ret = userns_call(fn_open_proc_r, UNS_FDOUT, path, ret + 1, -1);
>> +	else if (flags == O_WRONLY)
>> +		ret = userns_call(fn_open_proc_w, UNS_FDOUT, path, ret + 1, -1);
>> +	else if (flags == O_RDWR)
>> +		ret = userns_call(fn_open_proc_rw, UNS_FDOUT, path, ret + 1, -1);
>> +	else
>> +		BUG();
>> +	return ret;
>> +}
>>
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