From c97c2f4c26a8d23b7126e92c5b9663ee579e0f5f Mon Sep 17 00:00:00 2001
From: panxi39 <g200803092018@gmail.com>
Date: Sat, 13 Jun 2026 00:23:51 +0800
Subject: [PATCH] fix(linux): drop implicit DRM master for card fds

---
 src/platform/linux/cuda.cpp    |  4 +++
 src/platform/linux/kmsgrab.cpp |  4 +--
 src/platform/linux/misc.cpp    | 66 ++++++++++++++++++++++++++++++++++
 src/platform/linux/misc.h      |  6 ++++
 4 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/src/platform/linux/cuda.cpp b/src/platform/linux/cuda.cpp
index 9fd5e529b42..e775958d922 100644
--- a/src/platform/linux/cuda.cpp
+++ b/src/platform/linux/cuda.cpp
@@ -264,7 +264,11 @@ namespace cuda {
 
         fs::path dri_path {"/dev/dri"sv};
         auto device_path = dri_path / file;
+#ifdef SUNSHINE_BUILD_DRM
+        return platf::open_drm_card_fd_non_master(device_path.c_str());
+#else
         return open(device_path.c_str(), O_RDWR);
+#endif
       }
     } catch (const std::filesystem::filesystem_error &err) {
       BOOST_LOG(error) << "Failed to read sysfs: "sv << err.what();
diff --git a/src/platform/linux/kmsgrab.cpp b/src/platform/linux/kmsgrab.cpp
index 11571c7c361..903095bd9a7 100644
--- a/src/platform/linux/kmsgrab.cpp
+++ b/src/platform/linux/kmsgrab.cpp
@@ -320,10 +320,8 @@ namespace platf {
 
       int init(const char *path) {
         cap_sys_admin admin;
-        fd.el = open(path, O_RDWR);
-
+        fd.el = open_drm_card_fd_non_master(path);
         if (fd.el < 0) {
-          BOOST_LOG(error) << "Couldn't open: "sv << path << ": "sv << strerror(errno);
           return -1;
         }
 
diff --git a/src/platform/linux/misc.cpp b/src/platform/linux/misc.cpp
index 5f417810f6f..14e9c59bd75 100644
--- a/src/platform/linux/misc.cpp
+++ b/src/platform/linux/misc.cpp
@@ -9,6 +9,8 @@
 #endif
 
 // standard includes
+#include <cerrno>
+#include <cstring>
 #include <fstream>
 #include <iomanip>
 #include <iostream>
@@ -124,6 +126,70 @@ namespace dyn {
 namespace platf {
   using ifaddr_t = util::safe_ptr<ifaddrs, freeifaddrs>;
 
+#ifdef SUNSHINE_BUILD_DRM
+  int open_drm_card_fd_non_master(const char *path) {
+    int fd = open(path, O_RDWR | O_CLOEXEC);
+    if (fd < 0) {
+      BOOST_LOG(error) << "Couldn't open: "sv << path << ": "sv << strerror(errno);
+      return -1;
+    }
+
+    auto close_and_fail = [&]() {
+      close(fd);
+      return -1;
+    };
+
+    auto is_master = [&]() -> int {
+      drm_auth_t auth {};
+      auth.magic = 0;
+
+      errno = 0;
+      if (drmIoctl(fd, DRM_IOCTL_AUTH_MAGIC, &auth) == 0) {
+        return 1;
+      }
+
+      auto err = errno;
+      if (err == EACCES) {
+        return 0;
+      }
+
+      if (err == EINVAL || err == ENOENT) {
+        return 1;
+      }
+
+      BOOST_LOG(error) << "Couldn't determine DRM master state for "sv << path << ": "sv << strerror(err);
+      return -1;
+    };
+
+    auto master = is_master();
+    if (master < 0) {
+      return close_and_fail();
+    }
+
+    if (master) {
+      if (drmDropMaster(fd)) {
+        auto err = errno;
+        BOOST_LOG(error) << "Couldn't drop DRM master for "sv << path << ": "sv << strerror(err);
+        return close_and_fail();
+      }
+
+      BOOST_LOG(info) << "Dropped DRM master for "sv << path;
+
+      master = is_master();
+      if (master < 0) {
+        return close_and_fail();
+      }
+
+      if (master) {
+        BOOST_LOG(error) << "Still DRM master after drop: "sv << path;
+        return close_and_fail();
+      }
+    }
+
+    return fd;
+  }
+#endif
+
   ifaddr_t get_ifaddrs() {
     ifaddrs *p {nullptr};
 
diff --git a/src/platform/linux/misc.h b/src/platform/linux/misc.h
index c9f98f44de2..c22254bb68e 100644
--- a/src/platform/linux/misc.h
+++ b/src/platform/linux/misc.h
@@ -32,3 +32,9 @@ namespace dyn {
   void *handle(const std::vector<const char *> &libs);
 
 }  // namespace dyn
+
+#ifdef SUNSHINE_BUILD_DRM
+namespace platf {
+  int open_drm_card_fd_non_master(const char *path);
+}  // namespace platf
+#endif