libs/bsd: Implement getentropy(2).

With generic_syscall to avoid using a FD.

Change-Id: Id1702118bb673f06a861e4f0ad3401ce3d45cbd0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/31
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

Author: waddlesplash

headers/compatibility/bsd/unistd.h

@@ -28,6 +28,8 @@ char	*getusershell(void);
 int		issetugid(void);
 void	setusershell(void);
 
+int		getentropy(void *buf, size_t buflen);
+
 #ifdef __cplusplus
 }
 #endif

headers/private/system/random_defs.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2023, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _KERNEL_RANDOM_DEFS_H
+#define _KERNEL_RANDOM_DEFS_H
+
+
+#include <stddef.h>
+
+
+#define RANDOM_SYSCALLS			"random"
+#define RANDOM_GET_ENTROPY		1
+
+
+struct random_get_entropy_args {
+	void* buffer;
+	size_t length;
+};
+
+
+#endif	/* _KERNEL_RANDOM_DEFS_H */

src/add-ons/kernel/bus_managers/random/driver.cpp

@@ -13,7 +13,10 @@
 
 #include <device_manager.h>
 #include <Drivers.h>
+#include <generic_syscall.h>
+#include <kernel.h>
 #include <malloc.h>
+#include <random_defs.h>
 #include <string.h>
 #include <util/AutoLock.h>
 
@@ -103,6 +106,33 @@ random_control(void *cookie, uint32 op, void *arg, size_t length)
 }
 
 
+static status_t
+random_generic_syscall(const char* subsystem, uint32 function, void* buffer,
+	size_t bufferSize)
+{
+	switch (function) {
+		case RANDOM_GET_ENTROPY:
+		{
+			random_get_entropy_args args;
+			if (bufferSize != sizeof(args) || !IS_USER_ADDRESS(buffer))
+				return B_BAD_VALUE;
+
+			if (user_memcpy(&args, buffer, sizeof(args)) != B_OK)
+				return B_BAD_ADDRESS;
+			if (!IS_USER_ADDRESS(args.buffer))
+				return B_BAD_ADDRESS;
+
+			status_t result = random_read(NULL, 0, args.buffer, &args.length);
+			if (result < 0)
+				return result;
+
+			return user_memcpy(buffer, &args, sizeof(args));
+		}
+	}
+	return B_BAD_HANDLER;
+}
+
+
 static status_t
 random_close(void *cookie)
 {
@@ -197,6 +227,8 @@ random_init_driver(device_node *node, void **cookie)
 
 	info->node = node;
 
+	register_generic_syscall(RANDOM_SYSCALLS, random_generic_syscall, 1, 0);
+
 	*cookie = info;
 	return B_OK;
 }
@@ -207,6 +239,8 @@ random_uninit_driver(void *_cookie)
 {
 	CALLED();
 
+	unregister_generic_syscall(RANDOM_SYSCALLS, 1);
+
 	RANDOM_UNINIT();
 
 	mutex_destroy(&sRandomLock);

src/libs/bsd/Jamfile

@@ -17,6 +17,7 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 			explicit_bzero.c
 			fgetln.c
 			fts.c
+			getentropy.c
 			getpass.c
 			issetugid.c
 			kqueue.cpp

src/libs/bsd/getentropy.c

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2023, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+
+#include <unistd.h>
+
+#include <libroot/errno_private.h>
+#include <random_defs.h>
+#include <syscalls.h>
+
+
+int
+getentropy(void *buf, size_t buflen)
+{
+	status_t status;
+	struct random_get_entropy_args args;
+	args.buffer = buf;
+	args.length = buflen;
+
+	status = _kern_generic_syscall(RANDOM_SYSCALLS, RANDOM_GET_ENTROPY,
+		&args, sizeof(args));
+	if (args.length < buflen)
+		status = EIO;
+
+	if (status < 0) {
+		__set_errno(status);
+		return -1;
+	}
+	return 0;
+}