Add initial code for syscall redirection, fix path lookup failures.

pathmapping/pathmapping_interf.c

@@ -249,15 +249,12 @@ void sbox_map_path_at(
 		res->mres_readonly = 1;
 		return;
 	}
-        if (*virtual_path == '\0') {
-		goto end;
-	}
 
-	if ((*virtual_path == '/')
+	if (virtual_path && ((*virtual_path == '/')
 #ifdef AT_FDCWD
-	    || (dirfd == AT_FDCWD)
+		|| (dirfd == AT_FDCWD)
 #endif
-	   ) {
+	   )) {
 		/* same as sbox_map_path() */
 		fwd_map_path(
 			(sbox_binary_name ? sbox_binary_name : "UNKNOWN"),
@@ -273,9 +270,16 @@ void sbox_map_path_at(
 		/* pathname found */
 		char *virtual_abs_path_at_fd = NULL;
 
-		if (asprintf(&virtual_abs_path_at_fd, "%s/%s", dirfd_path, virtual_path) < 0) {
-			/* asprintf failed */
-			abort();
+		if (!virtual_path || *virtual_path == '\0') {
+			if (asprintf(&virtual_abs_path_at_fd, "%s", dirfd_path) < 0) {
+				/* asprintf failed */
+				abort();
+			}
+		} else {
+			if (asprintf(&virtual_abs_path_at_fd, "%s/%s", dirfd_path, virtual_path) < 0) {
+				/* asprintf failed */
+				abort();
+			}
 		}
 		SB_LOG(SB_LOGLEVEL_DEBUG,
 			"Synthetic path for %s(%d,'%s') => '%s'",
@@ -290,12 +294,11 @@ void sbox_map_path_at(
 		return;
 	}
 
-end:
 	/* name not found. Can't do much here, log a warning and return
 	 * the original relative path. That will work if we are lucky, but
 	 * not always..  */
 	SB_LOG(SB_LOGLEVEL_WARNING, "Path not found for FD %d, for %s(%s)",
-		dirfd, func_name, virtual_path);
+			dirfd, func_name, virtual_path);
 	res->mres_result_buf = res->mres_result_path = strdup(virtual_path);
 	res->mres_readonly = 0;
 }

preload/Makefile

@@ -11,6 +11,7 @@ objs := wrappers.o privatewrappers.o \
 	fdpathdb.o procfs.o mempcpy.o \
 	union_dirs.o \
 	system.o \
+	syscalls.o \
 	sb2context.o
 
 ifeq ($(shell uname -s),Linux)

preload/interface.master

@@ -111,6 +111,8 @@ GATE: int execve (const char *filename, char *const argv [], char *const envp[])
 GATE: int execvp (const char *file, char *const argv [])
 GATE: int execvpe(const char *file, char *const argv[], char *const envp[])
 
+GATE: long syscall(long number, ...) : pass_va_list
+
 GATE: int posix_spawn (pid_t *pid, const char *path, \
                        const posix_spawn_file_actions_t *file_actions, \
                        const posix_spawnattr_t *attrp, \

preload/syscalls.c

@@ -0,0 +1,100 @@
+/*
+ *
+ * SPDX-FileCopyrightText: 2023, Jolla Ltd.
+ * SPDX-License-Identifier: LGPL-2.1
+ *
+ * syscallgate -- syscall() GATE for the scratchbox2 preload library
+ *
+ * Copyright (C) 2023 Jolla Ltd.
+ */
+
+#include <asm-generic/unistd.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "libsb2.h"
+#include "exported.h"
+
+#define EXPAND_0(OPERATION)
+#define EXPAND_1(OPERATION, X) OPERATION(X)
+#define EXPAND_2(OPERATION, X, ...) OPERATION(X)EXPAND_1(OPERATION, __VA_ARGS__)
+#define EXPAND_3(OPERATION, X, ...) OPERATION(X)EXPAND_2(OPERATION, __VA_ARGS__)
+#define EXPAND_4(OPERATION, X, ...) OPERATION(X)EXPAND_3(OPERATION, __VA_ARGS__)
+#define EXPAND_5(OPERATION, X, ...) OPERATION(X)EXPAND_4(OPERATION, __VA_ARGS__)
+#define EXPAND_6(OPERATION, X, ...) OPERATION(X)EXPAND_5(OPERATION, __VA_ARGS__)
+
+#define GET_MACRO(_0,_1,_2,_3,_4,_5,_6,NAME,...) NAME
+#define FOR_EACH(action,...) \
+  GET_MACRO(_0,__VA_ARGS__,EXPAND_6,EXPAND_5,EXPAND_4,EXPAND_3,EXPAND_2,EXPAND_1,EXPAND_0)(action,__VA_ARGS__)
+
+#define DEFINE_ARG(arg) long arg = va_arg(args, long);
+
+#define FORWARD_TO_WRAPPER(sysc, ...) \
+		case SYS_ ## sysc: { \
+			FOR_EACH(DEFINE_ARG, __VA_ARGS__); \
+			ret = sysc(__VA_ARGS__); \
+		} break
+
+extern long syscall_gate(int *result_errno_ptr,
+	long (*real_syscall_ptr)(long number, ...),
+	const char *realfnname, long number, va_list args)
+{
+	long ret;
+	switch (number) {
+		FORWARD_TO_WRAPPER(execve, arg0, arg1, arg2);
+		FORWARD_TO_WRAPPER(openat, arg0, arg1, arg2, arg3);
+		// FORWARD_TO_WRAPPER(open_by_handle_at, ...)
+		FORWARD_TO_WRAPPER(open, arg0, arg1, arg2);
+		FORWARD_TO_WRAPPER(renameat, arg0, arg1, arg2, arg3);
+		FORWARD_TO_WRAPPER(renameat2, arg0, arg1, arg2, arg3, arg4);
+		FORWARD_TO_WRAPPER(connect, arg0, arg1, arg2);
+		FORWARD_TO_WRAPPER(sendto, arg0, arg1, arg2, arg3, arg4, arg5);
+		FORWARD_TO_WRAPPER(sendmsg, arg0, arg1, arg2);
+		case SYS_recvfrom: {
+			FOR_EACH(DEFINE_ARG, arg0, arg1, arg2, arg3, arg4, arg5);
+			// must do a cast...
+			ret = recvfrom(arg0, arg1, arg2, arg3, (struct sockaddr*)arg4, arg5);
+			break;
+		}
+		FORWARD_TO_WRAPPER(recvmsg, arg0, arg1, arg2);
+		FORWARD_TO_WRAPPER(accept, arg0, arg1, arg2);
+		FORWARD_TO_WRAPPER(accept4, arg0, arg1, arg2, arg3);
+		FORWARD_TO_WRAPPER(utimensat, arg0, arg1, arg2, arg3);
+		FORWARD_TO_WRAPPER(utime, arg0, arg1);
+		FORWARD_TO_WRAPPER(utimes, arg0, arg1);
+		FORWARD_TO_WRAPPER(fcntl, arg0, arg1, arg2);
+		FORWARD_TO_WRAPPER(futimesat, arg0, arg1, arg2);
+
+#ifdef SYS_wait
+		FORWARD_TO_WRAPPER(wait, arg0);
+#endif
+		FORWARD_TO_WRAPPER(waitpid, arg0, arg1, arg2);
+
+#ifdef SYS_wait3
+		case SYS_wait3: {
+			FOR_EACH(DEFINE_ARG, arg0, arg1, arg2);
+			// different number of arguments (for now we ignore rusage
+			// and redirect to waitpid).
+			ret = waitpid(-1, arg0, arg1);
+			break;
+		}
+#endif
+
+		case SYS_wait4: {
+			FOR_EACH(DEFINE_ARG, arg0, arg1, arg2, arg3);
+			// different number of arguments (for now we ignore rusage
+			// and redirect to waitpid).
+			ret = waitpid(arg0, arg1, arg2);
+			break;
+		}
+
+		default: {
+			FOR_EACH(DEFINE_ARG, arg0, arg1, arg2, arg3, arg4, arg5);
+			ret = real_syscall_ptr(number, arg0, arg1, arg2, arg3, arg4, arg5);
+			break;
+		}
+	};
+	if (result_errno_ptr) *result_errno_ptr = errno;
+	return ret;
+}
+