1 files changed, 61 insertions, 0 deletions
diff --git a/libc-top-half/musl/src/unistd/faccessat.c b/libc-top-half/musl/src/unistd/faccessat.c
new file mode 100644
index 0000000..557503e
--- /dev/null
+++ b/libc-top-half/musl/src/unistd/faccessat.c
@@ -0,0 +1,61 @@
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/wait.h>
+#include "syscall.h"
+#include "pthread_impl.h"
+
+struct ctx {
+	int fd;
+	const char *filename;
+	int amode;
+	int p;
+};
+
+static int checker(void *p)
+{
+	struct ctx *c = p;
+	int ret;
+	if (__syscall(SYS_setregid, __syscall(SYS_getegid), -1)
+	    || __syscall(SYS_setreuid, __syscall(SYS_geteuid), -1))
+		__syscall(SYS_exit, 1);
+	ret = __syscall(SYS_faccessat, c->fd, c->filename, c->amode, 0);
+	__syscall(SYS_write, c->p, &ret, sizeof ret);
+	return 0;
+}
+
+int faccessat(int fd, const char *filename, int amode, int flag)
+{
+	if (flag) {
+		int ret = __syscall(SYS_faccessat2, fd, filename, amode, flag);
+		if (ret != -ENOSYS) return __syscall_ret(ret);
+	}
+
+	if (flag & ~AT_EACCESS)
+		return __syscall_ret(-EINVAL);
+
+	if (!flag || (getuid()==geteuid() && getgid()==getegid()))
+		return syscall(SYS_faccessat, fd, filename, amode);
+
+	char stack[1024];
+	sigset_t set;
+	pid_t pid;
+	int status;
+	int ret, p[2];
+
+	if (pipe2(p, O_CLOEXEC)) return __syscall_ret(-EBUSY);
+	struct ctx c = { .fd = fd, .filename = filename, .amode = amode, .p = p[1] };
+
+	__block_all_sigs(&set);
+	
+	pid = __clone(checker, stack+sizeof stack, 0, &c);
+	__syscall(SYS_close, p[1]);
+
+	if (pid<0 || __syscall(SYS_read, p[0], &ret, sizeof ret) != sizeof(ret))
+		ret = -EBUSY;
+	__syscall(SYS_close, p[0]);
+	__syscall(SYS_wait4, pid, &status, __WCLONE, 0);
+
+	__restore_sigs(&set);
+
+	return __syscall_ret(ret);
+}