1 files changed, 99 insertions, 0 deletions

diff --git a/libs/binder/OS.cpp b/libs/binder/OS.cpp
index 24ce2bb465..77e401f83e 100644
--- a/libs/binder/OS.cpp
+++ b/libs/binder/OS.cpp
@@ -18,6 +18,7 @@
 
 #include <android-base/file.h>
 #include <binder/RpcTransportRaw.h>
+#include <log/log.h>
 #include <string.h>
 
 using android::base::ErrnoError;
@@ -25,6 +26,9 @@ using android::base::Result;
 
 namespace android {
 
+// Linux kernel supports up to 253 (from SCM_MAX_FD) for unix sockets.
+constexpr size_t kMaxFdsPerMsg = 253;
+
 Result<void> setNonBlocking(android::base::borrowed_fd fd) {
     int flags = TEMP_FAILURE_RETRY(fcntl(fd.get(), F_GETFL));
     if (flags == -1) {
@@ -63,4 +67,99 @@ std::unique_ptr<RpcTransportCtxFactory> makeDefaultRpcTransportCtxFactory() {
     return RpcTransportCtxFactoryRaw::make();
 }
 
+int sendMessageOnSocket(
+        const RpcTransportFd& socket, iovec* iovs, int niovs,
+        const std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds) {
+    if (ancillaryFds != nullptr && !ancillaryFds->empty()) {
+        if (ancillaryFds->size() > kMaxFdsPerMsg) {
+            errno = EINVAL;
+            return -1;
+        }
+
+        // CMSG_DATA is not necessarily aligned, so we copy the FDs into a buffer and then
+        // use memcpy.
+        int fds[kMaxFdsPerMsg];
+        for (size_t i = 0; i < ancillaryFds->size(); i++) {
+            fds[i] = std::visit([](const auto& fd) { return fd.get(); }, ancillaryFds->at(i));
+        }
+        const size_t fdsByteSize = sizeof(int) * ancillaryFds->size();
+
+        alignas(struct cmsghdr) char msgControlBuf[CMSG_SPACE(sizeof(int) * kMaxFdsPerMsg)];
+
+        msghdr msg{
+                .msg_iov = iovs,
+                .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+                .msg_control = msgControlBuf,
+                .msg_controllen = sizeof(msgControlBuf),
+        };
+
+        cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
+        cmsg->cmsg_level = SOL_SOCKET;
+        cmsg->cmsg_type = SCM_RIGHTS;
+        cmsg->cmsg_len = CMSG_LEN(fdsByteSize);
+        memcpy(CMSG_DATA(cmsg), fds, fdsByteSize);
+
+        msg.msg_controllen = CMSG_SPACE(fdsByteSize);
+        return TEMP_FAILURE_RETRY(sendmsg(socket.fd.get(), &msg, MSG_NOSIGNAL | MSG_CMSG_CLOEXEC));
+    }
+
+    msghdr msg{
+            .msg_iov = iovs,
+            // posix uses int, glibc uses size_t.  niovs is a
+            // non-negative int and can be cast to either.
+            .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+    };
+    return TEMP_FAILURE_RETRY(sendmsg(socket.fd.get(), &msg, MSG_NOSIGNAL));
+}
+
+int receiveMessageFromSocket(
+        const RpcTransportFd& socket, iovec* iovs, int niovs,
+        std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds) {
+    if (ancillaryFds != nullptr) {
+        int fdBuffer[kMaxFdsPerMsg];
+        alignas(struct cmsghdr) char msgControlBuf[CMSG_SPACE(sizeof(fdBuffer))];
+
+        msghdr msg{
+                .msg_iov = iovs,
+                .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+                .msg_control = msgControlBuf,
+                .msg_controllen = sizeof(msgControlBuf),
+        };
+        ssize_t processSize = TEMP_FAILURE_RETRY(recvmsg(socket.fd.get(), &msg, MSG_NOSIGNAL));
+        if (processSize < 0) {
+            return -1;
+        }
+
+        for (cmsghdr* cmsg = CMSG_FIRSTHDR(&msg); cmsg != nullptr; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+            if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
+                // NOTE: It is tempting to reinterpret_cast, but cmsg(3) explicitly asks
+                // application devs to memcpy the data to ensure memory alignment.
+                size_t dataLen = cmsg->cmsg_len - CMSG_LEN(0);
+                LOG_ALWAYS_FATAL_IF(dataLen > sizeof(fdBuffer)); // validity check
+                memcpy(fdBuffer, CMSG_DATA(cmsg), dataLen);
+                size_t fdCount = dataLen / sizeof(int);
+                ancillaryFds->reserve(ancillaryFds->size() + fdCount);
+                for (size_t i = 0; i < fdCount; i++) {
+                    ancillaryFds->emplace_back(base::unique_fd(fdBuffer[i]));
+                }
+                break;
+            }
+        }
+
+        if (msg.msg_flags & MSG_CTRUNC) {
+            errno = EPIPE;
+            return -1;
+        }
+        return processSize;
+    }
+    msghdr msg{
+            .msg_iov = iovs,
+            // posix uses int, glibc uses size_t.  niovs is a
+            // non-negative int and can be cast to either.
+            .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+    };
+
+    return TEMP_FAILURE_RETRY(recvmsg(socket.fd.get(), &msg, MSG_NOSIGNAL));
+}
+
 } // namespace android