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#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <limits.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/sendfile.h>
#include <sys/capability.h>
static int readlink_realpath(const char *filepath, char *buffer) {
char symlinked_path[PATH_MAX];
ssize_t bytes_written = readlink(filepath, symlinked_path, sizeof(symlinked_path) - 1);
if(bytes_written == -1 && errno == EINVAL) {
/* Not a symlink */
strncpy(symlinked_path, filepath, sizeof(symlinked_path));
} else if(bytes_written == -1) {
return 0;
} else {
symlinked_path[bytes_written] = '\0';
}
if(!realpath(symlinked_path, buffer))
return 0;
return 1;
}
static int file_has_sys_admin_capability(const char *filepath) {
cap_t cap = cap_get_file(filepath);
if(!cap)
return 0;
cap_flag_value_t res = CAP_CLEAR;
cap_get_flag(cap, CAP_SYS_ADMIN, CAP_PERMITTED, &res);
int cap_set = res == CAP_SET;
cap_free(cap);
return cap_set;
}
static int file_set_sys_admin_capability(const char *filepath, int setfcap) {
cap_t cap = cap_get_file(filepath);
if(!cap && errno != ENODATA)
return 0;
if(!cap) {
cap = cap_init();
if(!cap)
return 0;
}
const cap_value_t cap_to_set[] = { CAP_SYS_ADMIN, CAP_SETFCAP };
int num_caps = 1;
if(setfcap)
num_caps = 2;
int res = 0;
res |= cap_set_flag(cap, CAP_EFFECTIVE, num_caps, cap_to_set, CAP_SET);
res |= cap_set_flag(cap, CAP_PERMITTED, num_caps, cap_to_set, CAP_SET);
/*cap_set_flag(cap, CAP_INHERITABLE, num_caps, cap_to_set, CAP_SET);*/
res |= cap_set_file(filepath, cap);
cap_free(cap);
return res == 0;
}
static int create_local_kms_server_proxy_directory(const char *home) {
char path[PATH_MAX];
int err;
const char *paths[] = { ".local", ".local/share", ".local/share/gpu-screen-recorder", NULL };
for(size_t i = 0; paths[i]; ++i) {
const char *path_part = paths[i];
snprintf(path, sizeof(path), "%s/%s", home, path_part);
err = mkdir(path, S_IRWXU);
if(err == -1 && errno != EEXIST)
return 0;
}
return 1;
}
static int create_local_kms_server_proxy_file_atomic(const char *source_path, const char *dest_path) {
int in_fd = -1;
int out_fd = -1;
int res = 0;
char tmp_filepath[PATH_MAX];
snprintf(tmp_filepath, sizeof(tmp_filepath), "%s.tmp", dest_path);
in_fd = open(source_path, O_RDONLY);
if(in_fd == -1)
goto done;
struct stat st;
if(fstat(in_fd, &st) == -1)
goto done;
out_fd = open(tmp_filepath, O_RDWR | O_CREAT | O_TRUNC, 0755);
if(out_fd == -1)
goto done;
if(sendfile(out_fd, in_fd, NULL, st.st_size) != st.st_size)
goto done;
res = 1;
done:
if(in_fd)
close(in_fd);
if(out_fd)
close(out_fd);
if(res)
res = file_set_sys_admin_capability(tmp_filepath, 1);
if(res)
rename(tmp_filepath, dest_path);
return res;
}
int main(int argc, char **argv) {
if(argc != 4) {
fprintf(stderr, "usage: kms-server-proxy <initial_socket_path> <card_path> <user_homepath>\n");
return 1;
}
const char *gsr_kms_server_filepath = "/var/lib/flatpak/app/com.dec05eba.gpu_screen_recorder/current/active/files/bin/gsr-kms-server";
const char *initial_socket_path = argv[1];
const char *card_path = argv[2];
const char *user_homepath = argv[3];
char self_path[PATH_MAX];
if(!readlink_realpath("/proc/self/exe", self_path)) {
fprintf(stderr, "failed to resolve /proc/self/exe\n");
return 1;
}
char kms_server_proxy_local_filepath[PATH_MAX];
/* Update kms-server-proxy-N to kms-server-proxy-N+1 on update (update that needs to run before this program launches itself) */
snprintf(kms_server_proxy_local_filepath, sizeof(kms_server_proxy_local_filepath), "%s/.local/share/gpu-screen-recorder/kms-server-proxy-1", user_homepath);
if(file_has_sys_admin_capability(gsr_kms_server_filepath)) {
const char *args[] = { gsr_kms_server_filepath, initial_socket_path, card_path, NULL };
return execv(args[0], (char *const*)args);
} else if(file_has_sys_admin_capability(kms_server_proxy_local_filepath)) {
/* Need to resolve kms_server_proxy_local_filepath because /home can be a symlink to another location */
char kms_server_proxy_local_filepath_full[PATH_MAX];
if(!readlink_realpath(kms_server_proxy_local_filepath, kms_server_proxy_local_filepath_full)) {
fprintf(stderr, "failed to resolve %s\n", kms_server_proxy_local_filepath);
return 1;
}
/*
Run cached ~/.local/share/gpu-screen-recorder/kms-server-proxy which has sys admin capability.
The one in flatpak location gets capabilities overwritten on flatpak update.
*/
if(strcmp(self_path, kms_server_proxy_local_filepath_full) != 0) {
const char *args[] = { kms_server_proxy_local_filepath_full, initial_socket_path, card_path, user_homepath, NULL };
return execv(args[0], (char *const*)args);
}
/* TODO: Remove the need for this. Instead inherit capabilities */
if(file_set_sys_admin_capability(gsr_kms_server_filepath, 0)) {
const char *args[] = { gsr_kms_server_filepath, initial_socket_path, card_path, NULL };
return execv(args[0], (char *const*)args);
}
const char *args[] = { "pkexec", gsr_kms_server_filepath, initial_socket_path, card_path, NULL };
return execvp(args[0], (char *const*)args);
} else if(geteuid() == 0) { /* is current user root */
file_set_sys_admin_capability(gsr_kms_server_filepath, 0);
create_local_kms_server_proxy_file_atomic(self_path, kms_server_proxy_local_filepath);
const char *args[] = { gsr_kms_server_filepath, initial_socket_path, card_path, NULL };
return execv(args[0], (char *const*)args);
} else {
create_local_kms_server_proxy_directory(user_homepath);
const char *args[] = { "pkexec", self_path, initial_socket_path, card_path, user_homepath, NULL };
return execvp(args[0], (char *const*)args);
}
}
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