lib: utils: implement internal safe_strcpy function

The strlcpy() function has only recently become available in glibc.
While this function prevents destination buffer overflow, it seems
that it cannot guarantee read access only within the source buffer.
this is for instance the case if the source string is not terminated by
a'\0' character.
Implement a safe_strcpy to ensure that no access is done out of the
source and destination buffer ranges.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

lib/CMakeLists.txt

@@ -10,6 +10,7 @@ collect (PROJECT_LIB_SOURCES version.c)
 add_subdirectory (virtio)
 add_subdirectory (rpmsg)
 add_subdirectory (remoteproc)
+add_subdirectory (utils)
 if (WITH_VIRTIO_MMIO_DRV)
 add_subdirectory (virtio_mmio)
 endif (WITH_VIRTIO_MMIO_DRV)
@@ -23,6 +24,7 @@ set (OPENAMP_LIB open_amp)
 
 configure_file(version.h.in ${PROJECT_BINARY_DIR}/include/generated/openamp/version_def.h)
 collect (PROJECT_INC_DIRS " ${PROJECT_BINARY_DIR}/include/generated/openamp")
+collect (PROJECT_INC_DIRS " ${PROJECT_BINARY_DIR}/include/internal")
 
 if (NOT CMAKE_INSTALL_LIBDIR)
 	set (CMAKE_INSTALL_LIBDIR "lib")

lib/include/internal/utilities.h

@@ -0,0 +1,35 @@
+/*
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2024, STMicroelectronics
+ *
+ */
+
+#include <string.h>
+
+/**
+ * @internal
+ *
+ * @brief Copies a string to a destination buffer with size limitation and returns the length of
+ *        the destination string.
+ *
+ * This function copies up to `s_size - 1` characters from the source string `src`
+ * to the destination buffer `dst`, ensuring that the destination buffer is
+ * null-terminated. The function returns the length of the `dst` string.
+ * If the length of `src` string is greater than or equal to `d_size`, the destination
+ * buffer will be truncated.
+ *
+ * @param dst    Destination buffer where the string will be copied.
+ * @param d_size Size of the destination buffer.
+ * @param src    Source string to be copied.
+ * @param s_size Size of the source buffer.
+ * @return       The length of the string contained in the `dst` buffer.
+ *
+ * @note If the size of the destination buffer is 0, the function does not copy any characters and
+ *       the destination buffer is not null-terminated.
+ * @note The function ensures that the destination buffer is always null-terminated if `size` is
+ *       greater than 0.
+ * @note The function ensures that no data is read past the end of the 'src' buffer.
+ */
+size_t safe_strcpy(char *dst, size_t d_size, const char *src, size_t s_size);
+

lib/utils/CMakeLists.txt

@@ -0,0 +1 @@
+collect (PROJECT_LIB_SOURCES utilities.c)

lib/utils/utilities.c

@@ -0,0 +1,35 @@
+/*
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2024, STMicroelectronics
+ *
+ */
+
+#include <internal/utilities.h>
+#include <metal/io.h>
+#include <metal/utilities.h>
+
+size_t safe_strcpy(char *dst, size_t d_size, const char *src, size_t s_size)
+{
+	size_t size = metal_min(s_size, d_size);
+	size_t nleft = size + 1;
+	char *d = dst;
+
+	if (!d_size)
+		return 0;
+
+	/* Copy as many bytes as will fit. */
+	while (--nleft != 0) {
+		*dst = *src++;
+		if (*dst++ == '\0')
+			break;
+	}
+
+	/* Fill last characters with '\0' */
+	if (size < d_size)
+		memset(dst, '\0',  d_size - size + nleft);
+	else
+		d[d_size - 1] = '\0';
+
+	return size - nleft;
+}