Rainer Weikusat <rw@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
> Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx> writes:
>> On 02/05/2016 02:59 PM, Rainer Weikusat wrote:
>
> [recvmsg w/o iovecs returning ENOTSUP for CMSG requests]
[...]
> There are more problems wrt handling control-message only reads in this
> code.
[...]
> it will return without an error but also without credentials if the
[...]
> because the following
>
> mutex_lock(&u->readlock);
> continue;
>
> will cause the
>
> do {
> } while (size)
>
> loop condition to be evaluated and since size is 0 (AIUI), the loop will
> terminate immediately.
As I suspected, the test program included below doesn't really receive
the credentials (tested with a 4.5.0-rc2-net w/ the previous patch
applied). As that's a minor, additional problem, I'll fix that, too.
---
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <assert.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
int main(void)
{
enum { server, client, size };
int socket_fd[size];
int const opt = 1;
assert(socketpair(AF_LOCAL, SOCK_STREAM, 0, socket_fd) == 0);
assert(setsockopt(socket_fd[server], SOL_SOCKET, SO_PASSCRED, &opt, sizeof(opt)) != -1);
char const msg[] = "A random message";
if (fork() == 0) {
sleep(1);
send(socket_fd[client], msg, sizeof msg, MSG_DONTWAIT | MSG_NOSIGNAL);
_exit(0);
}
union {
struct cmsghdr cmh;
char control[CMSG_SPACE(sizeof(struct ucred))];
} control_un;
control_un.cmh.cmsg_len = CMSG_LEN(sizeof(struct ucred));
control_un.cmh.cmsg_level = SOL_SOCKET;
control_un.cmh.cmsg_type = SCM_CREDENTIALS;
struct msghdr msgh;
msgh.msg_name = NULL;
msgh.msg_namelen = 0;
msgh.msg_iov = NULL;
msgh.msg_iovlen = 0;
msgh.msg_control = control_un.control;
msgh.msg_controllen = sizeof(control_un.control);
if (recvmsg(socket_fd[server], &msgh, MSG_PEEK) == -1)
{
printf("Error: %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
else
{
struct ucred *ucred;
printf("Success?\n");
ucred = (void *)CMSG_DATA(&control_un.cmh);
printf("... pid %ld, uid %d, gid %d\n",
(long)ucred->pid, ucred->uid, ucred->gid);
}
return 0;
}
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