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fix(linux/xdgportal): Improve multi-monitor support and work around breaking kmsgrab #4969

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Merged
ReenigneArcher merged 3 commits into from
Apr 10, 2026
+81 −54
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fix(linux/xdgportal): Improve multi-monitor support and work around breaking kmsgrab #4969

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cd31cdf
fix(linux/xdgportal): Improve pipewire stream selection and sorting
Kishi85 Apr 10, 2026
71c055c
fix(linux/xdgportal): Drop CAP_SYS_ADMIN when initializing the first …
Kishi85 Apr 10, 2026
1b88786
refactor(linux/xdgportal): Rename session_cache_t to runtime_t
Kishi85 Apr 10, 2026
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135 changes: 81 additions & 54 deletions src/platform/linux/portalgrab.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -72,7 +72,7 @@ using namespace std::literals;

namespace portal {
// Forward declarations
class session_cache_t;
class runtime_t;

class restore_token_t {
public:
Expand Down Expand Up @@ -173,15 +173,15 @@ namespace portal {
};

struct pipewire_streaminfo_t {
int pipewire_node;
int width;
int height;
int pos_x;
int pos_y;
int pipewire_node = -1;
int width = 0;
int height = 0;
int pos_x = 0;
int pos_y = 0;
std::string monitor_name;

std::string to_display_name() {
if (monitor_name.length() > 0) {
if (!monitor_name.empty()) {
return std::format("n{}", monitor_name);
}
return std::format("p{},{},{},{}", pos_x, pos_y, width, height);
Expand Down Expand Up @@ -287,44 +287,12 @@ namespace portal {
return 0;
}

void finalize_portal_security() {
#if !defined(__FreeBSD__)
BOOST_LOG(debug) << "[portalgrab] Finalizing Portal security: dropping capabilities and resetting dumpable"sv;

cap_t caps = cap_get_proc();
if (!caps) {
BOOST_LOG(error) << "[portalgrab] Failed to get process capabilities"sv;
return;
}

std::array<cap_value_t, 2> effective_list {CAP_SYS_ADMIN, CAP_SYS_NICE};
std::array<cap_value_t, 2> permitted_list {CAP_SYS_ADMIN, CAP_SYS_NICE};

cap_set_flag(caps, CAP_EFFECTIVE, effective_list.size(), effective_list.data(), CAP_CLEAR);
cap_set_flag(caps, CAP_PERMITTED, permitted_list.size(), permitted_list.data(), CAP_CLEAR);

if (cap_set_proc(caps) != 0) {
BOOST_LOG(error) << "[portalgrab] Failed to prune capabilities: "sv << std::strerror(errno);
}
cap_free(caps);

// Reset dumpable AFTER the caps have been pruned to ensure the Portal can
// access /proc/pid/root.
if (prctl(PR_SET_DUMPABLE, 1) != 0) {
BOOST_LOG(error) << "[portalgrab] Failed to set PR_SET_DUMPABLE: "sv << std::strerror(errno);
}
#endif
}

int connect_to_portal() {
g_autoptr(GMainLoop) loop = g_main_loop_new(nullptr, FALSE);
g_autofree gchar *session_path = nullptr;
g_autofree gchar *session_token = nullptr;
create_session_path(conn, nullptr, &session_token);

// Drop CAP_SYS_ADMIN and set DUMPABLE flag to allow XDG /root access
finalize_portal_security();

// Try combined RemoteDesktop + ScreenCast session first
bool use_screencast_only = !try_remote_desktop_session(loop, &session_path, session_token);

Expand Down Expand Up @@ -655,12 +623,20 @@ namespace portal {
while (g_variant_iter_next(&iter, "(u@a{sv})", &out_pipewire_node, &value)) {
int out_width;
int out_height;
g_variant_lookup(value, "size", "(ii)", &out_width, &out_height, nullptr);
bool result = g_variant_lookup(value, "size", "(ii)", &out_width, &out_height, nullptr);
if (!result) {
BOOST_LOG(warning) << "[portalgrab] Ignoring stream without proper resolution on pipewire node "sv << out_pipewire_node;
continue;
}

int out_pos_x;
int out_pos_y;
g_variant_lookup(value, "position", "(ii)", &out_pos_x, &out_pos_y, nullptr);

result = g_variant_lookup(value, "position", "(ii)", &out_pos_x, &out_pos_y, nullptr);
if (!result) {
BOOST_LOG(warning) << "[portalgrab] Falling back to position 0x0 for stream with resolution "sv << out_width << "x"sv << out_height << "on pipewire node "sv << out_pipewire_node;
out_pos_x = 0;
out_pos_y = 0;
}
auto stream = pipewire_streaminfo_t {out_pipewire_node, out_width, out_height, out_pos_x, out_pos_y};

// Try to match the stream to a monitor_name by position/resolution and update stream info
Expand All @@ -674,6 +650,12 @@ namespace portal {
out_pipewire_streams.emplace_back(stream);
}

// The portal call returns the streams sorted by out_pipewire_node which can shuffle displays around, so
// we have to sort pipewire streams by position here to be consistent
std::ranges::sort(out_pipewire_streams, [](const auto &a, const auto &b) {
return a.pos_x < b.pos_x || a.pos_y < b.pos_y;
});

return 0;
}

Expand Down Expand Up @@ -750,12 +732,12 @@ namespace portal {
};

/**
* @brief Singleton cache for persistent portalgrab session data.
* @brief Singleton for portalgrab stuff persistent during an application run.
*
*/
class session_cache_t {
class runtime_t {
public:
static session_cache_t &instance();
static runtime_t &instance();

bool is_maxframerate_failed() const {
return maxframerate_failed_;
Expand All @@ -765,19 +747,54 @@ namespace portal {
maxframerate_failed_ = true;
}

bool is_portal_secured() {
return is_portal_secured_;
}

void finalize_portal_security() {
#if !defined(__FreeBSD__)
BOOST_LOG(debug) << "[portalgrab] Finalizing Portal security: dropping capabilities and resetting dumpable"sv;

cap_t caps = cap_get_proc();
if (!caps) {
BOOST_LOG(error) << "[portalgrab] Failed to get process capabilities"sv;
return;
}

std::array<cap_value_t, 2> effective_list {CAP_SYS_ADMIN, CAP_SYS_NICE};
std::array<cap_value_t, 2> permitted_list {CAP_SYS_ADMIN, CAP_SYS_NICE};

cap_set_flag(caps, CAP_EFFECTIVE, effective_list.size(), effective_list.data(), CAP_CLEAR);
cap_set_flag(caps, CAP_PERMITTED, permitted_list.size(), permitted_list.data(), CAP_CLEAR);

if (cap_set_proc(caps) != 0) {
BOOST_LOG(error) << "[portalgrab] Failed to prune capabilities: "sv << std::strerror(errno);
}
cap_free(caps);

// Reset dumpable AFTER the caps have been pruned to ensure the Portal can
// access /proc/pid/root.
if (prctl(PR_SET_DUMPABLE, 1) != 0) {
BOOST_LOG(error) << "[portalgrab] Failed to set PR_SET_DUMPABLE: "sv << std::strerror(errno);
}
#endif
is_portal_secured_ = true;
}

private:
session_cache_t() = default;
runtime_t() = default;

// Prevent copying
session_cache_t(const session_cache_t &) = delete;
session_cache_t &operator=(const session_cache_t &) = delete;
runtime_t(const runtime_t &) = delete;
runtime_t &operator=(const runtime_t &) = delete;

bool maxframerate_failed_ = false;
bool is_portal_secured_ = false;
};

session_cache_t &session_cache_t::instance() {
alignas(session_cache_t) static std::array<std::byte, sizeof(session_cache_t)> storage;
static auto instance_ = new (storage.data()) session_cache_t();
runtime_t &runtime_t::instance() {
alignas(runtime_t) static std::array<std::byte, sizeof(runtime_t)> storage;
static auto instance_ = new (storage.data()) runtime_t();
return *instance_;
}

Expand Down Expand Up @@ -1050,7 +1067,7 @@ namespace portal {
spa_pod_builder_add(b, SPA_FORMAT_VIDEO_format, SPA_POD_Id(format), 0);
spa_pod_builder_add(b, SPA_FORMAT_VIDEO_size, SPA_POD_CHOICE_RANGE_Rectangle(&sizes[0], &sizes[1], &sizes[2]), 0);
spa_pod_builder_add(b, SPA_FORMAT_VIDEO_framerate, SPA_POD_Fraction(&framerates[0]), 0);
if (!session_cache_t::instance().is_maxframerate_failed()) {
if (!runtime_t::instance().is_maxframerate_failed()) {
spa_pod_builder_add(b, SPA_FORMAT_VIDEO_maxFramerate, SPA_POD_CHOICE_RANGE_Fraction(&framerates[0], &framerates[1], &framerates[2]), 0);
}

Expand Down Expand Up @@ -1103,9 +1120,9 @@ namespace portal {
}
break;
case PW_STREAM_STATE_ERROR:
if (old != PW_STREAM_STATE_STREAMING && !session_cache_t::instance().is_maxframerate_failed()) {
if (old != PW_STREAM_STATE_STREAMING && !runtime_t::instance().is_maxframerate_failed()) {
BOOST_LOG(warning) << "[portalgrab] Negotiation failed, will retry without maxFramerate"sv;
session_cache_t::instance().set_maxframerate_failed();
runtime_t::instance().set_maxframerate_failed();
}
[[fallthrough]];
case PW_STREAM_STATE_UNCONNECTED:
Expand Down Expand Up @@ -1676,6 +1693,9 @@ namespace platf {
return nullptr;
}

// Drop CAP_SYS_ADMIN and set DUMPABLE flag to allow XDG /root access
portal::runtime_t::instance().finalize_portal_security();

auto portal = std::make_shared<portal::portal_t>();
if (portal->init(hwdevice_type, display_name, config)) {
return nullptr;
Expand All @@ -1695,6 +1715,13 @@ namespace platf {

pw_init(nullptr, nullptr);

if (!portal::runtime_t::instance().is_portal_secured()) {
// We're still in the probing phase of Sunshine startup. Dropping portal security early will break KMS.
// Just return a dummy screen for now. Display re-enumeration after encoder probing will yield full result.
display_names.emplace_back("init");
return display_names;
}

if (dbus->connect_to_portal() < 0) {
BOOST_LOG(warning) << "[portalgrab] Failed to connect to portal. Cannot enumerate displays, returning empty list.";
return {};
Expand Down
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