Fix: kernel adds creds on recv with SO_PASSCRED unix socket option

[lttng-tools.git] / src / common / unix.c

diff --git a/src/common/unix.c b/src/common/unix.c
index 41525b69170a2c10bfcbdf2401f22936e576d058..3490af6e7d584d237d38ec6532d7b1fd93bcf1b1 100644 (file)
--- a/src/common/unix.c
+++ b/src/common/unix.c
@@ -385,7 +385,7 @@ ssize_t lttcomm_send_fds_unix_sock(int sock, const int *fds, size_t nb_fd)
        char dummy = 0;
 
        memset(&msg, 0, sizeof(msg));
-       memset(tmp, 0, CMSG_SPACE(sizeof_fds) * sizeof(char));
+       memset(tmp, 0, sizeof(tmp));
 
        if (nb_fd > LTTCOMM_MAX_SEND_FDS)
                return -EINVAL;
@@ -397,6 +397,7 @@ ssize_t lttcomm_send_fds_unix_sock(int sock, const int *fds, size_t nb_fd)
        if (!cmptr) {
                return -1;
        }
+
        cmptr->cmsg_level = SOL_SOCKET;
        cmptr->cmsg_type = SCM_RIGHTS;
        cmptr->cmsg_len = CMSG_LEN(sizeof_fds);
@@ -439,7 +440,9 @@ ssize_t lttcomm_recv_fds_unix_sock(int sock, int *fds, size_t nb_fd)
        ssize_t ret = 0;
        struct cmsghdr *cmsg;
        size_t sizeof_fds = nb_fd * sizeof(int);
-       char recv_fd[CMSG_SPACE(sizeof_fds)];
+
+       /* Account for the struct ucred cmsg in the buffer size */
+       char recv_buf[CMSG_SPACE(sizeof_fds) + CMSG_SPACE(sizeof(struct ucred))];
        struct msghdr msg;
        char dummy;
 
@@ -450,8 +453,15 @@ ssize_t lttcomm_recv_fds_unix_sock(int sock, int *fds, size_t nb_fd)
        iov[0].iov_len = 1;
        msg.msg_iov = iov;
        msg.msg_iovlen = 1;
-       msg.msg_control = recv_fd;
-       msg.msg_controllen = sizeof(recv_fd);
+
+       cmsg = (struct cmsghdr *) recv_buf;
+       cmsg->cmsg_len = CMSG_LEN(sizeof_fds);
+       cmsg->cmsg_level = SOL_SOCKET;
+       cmsg->cmsg_type = SCM_RIGHTS;
+
+       msg.msg_control = cmsg;
+       msg.msg_controllen = CMSG_LEN(sizeof(recv_buf));
+       msg.msg_flags = 0;
 
        do {
                ret = recvmsg(sock, &msg, 0);
@@ -460,35 +470,63 @@ ssize_t lttcomm_recv_fds_unix_sock(int sock, int *fds, size_t nb_fd)
                PERROR("recvmsg fds");
                goto end;
        }
+
        if (ret != 1) {
                fprintf(stderr, "Error: Received %zd bytes, expected %d\n",
                                ret, 1);
                goto end;
        }
+
        if (msg.msg_flags & MSG_CTRUNC) {
                fprintf(stderr, "Error: Control message truncated.\n");
                ret = -1;
                goto end;
        }
-       cmsg = CMSG_FIRSTHDR(&msg);
-       if (!cmsg) {
-               fprintf(stderr, "Error: Invalid control message header\n");
-               ret = -1;
-               goto end;
-       }
-       if (cmsg->cmsg_level != SOL_SOCKET || cmsg->cmsg_type != SCM_RIGHTS) {
-               fprintf(stderr, "Didn't received any fd\n");
-               ret = -1;
-               goto end;
-       }
-       if (cmsg->cmsg_len != CMSG_LEN(sizeof_fds)) {
-               fprintf(stderr, "Error: Received %zu bytes of ancillary data, expected %zu\n",
-                               (size_t) cmsg->cmsg_len, (size_t) CMSG_LEN(sizeof_fds));
-               ret = -1;
-               goto end;
+
+       /*
+        * If the socket was configured with SO_PASSCRED, the kernel will add a
+        * control message (cmsg) to the ancillary data of the unix socket. We
+        * need to expect a cmsg of the SCM_CREDENTIALS as the first control
+        * message.
+        */
+       for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+               if (!cmsg) {
+                       fprintf(stderr, "Error: Invalid control message header\n");
+                       ret = -1;
+                       goto end;
+               }
+               if (cmsg->cmsg_level != SOL_SOCKET) {
+                       fprintf(stderr, "Error: The socket needs to be of type SOL_SOCKET\n");
+                       ret = -1;
+                       goto end;
+               }
+               if (cmsg->cmsg_type == SCM_RIGHTS) {
+                       /*
+                        * We found the controle message for file descriptors,
+                        * now copy the fds to the fds ptr and return success.
+                        */
+                       if (cmsg->cmsg_len != CMSG_LEN(sizeof_fds)) {
+                               fprintf(stderr, "Error: Received %zu bytes of"
+                                       "ancillary data for FDs, expected %zu\n",
+                                       (size_t) cmsg->cmsg_len,
+                                       (size_t) CMSG_LEN(sizeof_fds));
+                               ret = -1;
+                               goto end;
+                       }
+                       memcpy(fds, CMSG_DATA(cmsg), sizeof_fds);
+                       ret = sizeof_fds;
+                       goto end;
+               }
+               if (cmsg->cmsg_type == SCM_CREDENTIALS) {
+                       /*
+                        * Expect credentials to be sent when expecting fds even
+                        * if no credential were include in the send(). The
+                        * kernel adds them...
+                        */
+                       fprintf(stderr, "Received creds... continuing\n");
+                       ret = -1;
+               }
        }
-       memcpy(fds, CMSG_DATA(cmsg), sizeof_fds);
-       ret = sizeof_fds;
 end:
        return ret;
 }