ELF32: RELRO, strip, linking info

README.md

@@ -4,3 +4,6 @@
 - display protections
 - colorful
 - maybe display elf sections if command entered (??)
+
+- security:
+enforce malloc secure fail

main.c

@@ -44,11 +44,16 @@
 #define PT_GNU_STACK   0x6474e551
 #define SHT_DYNSYM     11
 #define SHT_SYMTAB     2
+#define PT_GNU_RELRO   0x6474e552
+#define PT_DYNAMIC     2
+#define DT_BIND_NOW    24
+#define PT_INTERP      3
 
-#define Elf32_Half uint16_t
+#define Elf32_Half  uint16_t
-#define Elf32_Word uint32_t
+#define Elf32_Word  uint32_t
-#define Elf32_Addr uint32_t
+#define Elf32_Sword int32_t
-#define Elf32_Off  uint32_t
+#define Elf32_Addr  uint32_t
+#define Elf32_Off   uint32_t
 
 #define Elf64_Half uint32_t
 #define Elf64_Word uint64_t
@@ -59,6 +64,10 @@ bool verbose = false;
 bool pie = false;
 bool nx = false;
 bool canary = false;
+bool relro = false;
+bool bind_now = false;
+bool stripped = true;
+bool interp = false;
 
 struct Elf32_Ehdr
 {
@@ -114,6 +123,16 @@ struct Elf32_Sym
 	Elf32_Half st_shndx;
 };
 
+struct Elf32_Dyn
+{
+	Elf32_Sword d_tag;
+	union
+	{
+		Elf32_Word d_val;
+		Elf32_Addr d_ptr;
+	} d_un;
+} Elf32_Dyn;
+
 struct Elf64_Ehdr
 {
 	unsigned char e_ident[EI_NIDENT];
@@ -181,7 +200,41 @@ void display_elf_common(unsigned char e_ident[EI_NIDENT])
 	}
 }
 
-void display_elf32(struct Elf32_Ehdr* header)
+void check_dynamic32(struct Elf32_Ehdr* header, FILE* fp)
+{
+	// Is dynamically linked? (has PT_INTERP program header?)
+	// read program headers	
+	fseek(fp, header->e_phoff, SEEK_SET);
+	struct Elf32_Phdr *p_headers = malloc(header->e_phnum * sizeof(struct Elf32_Phdr));
+	fread(p_headers, sizeof(struct Elf32_Phdr), header->e_phnum, fp);
+
+	const char* interpstr = NULL;
+
+	for (int i=0; i<header->e_phnum; i++)
+	{
+		if (p_headers[i].p_type == PT_INTERP)
+		{
+			interp = true;
+
+			// Get interpreter path
+			interpstr = malloc(p_headers[i].p_filesz);
+			fseek(fp, p_headers[i].p_offset, SEEK_SET);
+			fread((char*)interpstr, 1, p_headers[i].p_filesz, fp);
+			break;
+		}
+	}
+
+	if (interp)
+	{
+		printf("dynamically linked (interpreter: %s), ", interpstr);
+	}
+	else
+	{
+		printf("statically linked, ");
+	}
+}
+
+void display_elf32(struct Elf32_Ehdr* header, FILE* fp)
 {
 	printf("32-bit ELF ");
 	display_elf_common(header->e_ident);
@@ -219,57 +272,51 @@ void display_elf32(struct Elf32_Ehdr* header)
 	switch (header->e_machine)
 	{
 		case 0x00:
-			printf("No architecture,");
+			printf("No architecture, ");
 			break;
 		case 0x01:
-			printf("AT&T WE 32100,");
+			printf("AT&T WE 32100, ");
 			break;
 		case 0x02:
-			printf("SPARC,");
+			printf("SPARC, ");
 			break;
 		case 0x03:
-			printf("i386,");
+			printf("i386, ");
 			break;
 		case 0x04:
-			printf("Motorola 68000,");
+			printf("Motorola 68000, ");
 			break;
 		case 0x05:
-			printf("Motorola 88000,");
+			printf("Motorola 88000, ");
 			break;
 		case 0x07:
-			printf("Intel 80860,");
+			printf("Intel 80860, ");
 			break;
 		case 0x08:
-			printf("MIPS RS3000,");
+			printf("MIPS RS3000, ");
 			break;
 		case 0x09:
-			printf("MIPS RS4000,");
+			printf("MIPS RS4000, ");
 			break;
 		default:
-			printf("Unknown architecture");
+			printf("Unknown architecture, ");
 			break;
 	}
 	
 	if (verbose)
 	{
-		printf("\ne_version:            %d\n", header->e_version);
+		check_dynamic32(header, fp);	
-		printf("e_entry:     0x%08x\n", header->e_entry);
-		printf("e_phoff:     0x%08x\n", header->e_phoff);
-		printf("e_shoff:     0x%08x\n", header->e_shoff);
-		printf("e_flags:     0x%08x\n", header->e_flags);
-		printf("e_ehsize:    0x%08x\n", header->e_ehsize);
-		printf("e_phentsize: 0x%08x\n", header->e_phentsize);
-		printf("e_phnum:     0x%08x\n", header->e_phnum);
-		printf("e_shentsize: 0x%08x\n", header->e_shentsize);
-		printf("e_shnum:     0x%08x\n", header->e_shnum);
-		printf("e_shstrndx:  0x%08x\n", header->e_shstrndx);
 	}
 }
 
+void check_nx32(struct Elf32_Ehdr* header, FILE* fp)
+{
+
+}
+
 void check_sec32(struct Elf32_Ehdr* header, FILE* fp)
 {
-
+	/* NX:
-	/*
 	 * Browse thru program header table (e_phnum items) from e_phoff (program header offset)
 	 * if its stack and has executable bit then we know NX isnt there
 	*/
@@ -291,7 +338,7 @@ void check_sec32(struct Elf32_Ehdr* header, FILE* fp)
 		}
 	}
 
-	/*
+	/* Stack canary:
 	 * Same for section header table (e_shnum items) from e_shoff (section header offset)
 	 * find sections .dynsym or .symtab:
 	 * and look for __stack_chk_fail (call for stack smashing)
@@ -310,6 +357,9 @@ void check_sec32(struct Elf32_Ehdr* header, FILE* fp)
 
 	for (size_t i=0; i<header->e_shnum; i++)
 	{
+		// additional small check for stripping as we're already browsing section headers
+		if (s_headers[i].sh_type == SHT_SYMTAB && s_headers[i].sh_size > 0) stripped = false;
+
 		if (s_headers[i].sh_type == SHT_DYNSYM || s_headers[i].sh_type == SHT_SYMTAB)
 		{
 			// load symbol table
@@ -335,6 +385,50 @@ void check_sec32(struct Elf32_Ehdr* header, FILE* fp)
 			}
 		}
 	}
+
+	/* RELRO:
+	 * Segment type PT_GNU_RELRO should be present
+	*/
+
+	// Read program headers
+	fseek(fp, header->e_phoff, SEEK_SET);
+	struct Elf32_Phdr *p_headers = malloc(header->e_phnum * sizeof(struct Elf32_Phdr));
+	fread (p_headers, sizeof(struct Elf32_Phdr), header->e_phnum, fp);
+
+	Elf32_Off dyn_off = 0;
+	Elf32_Word dyn_size = 0;
+
+	for (int i=0; i<header->e_phnum; i++)
+	{
+		if (p_headers[i].p_type == PT_GNU_RELRO)
+		{
+			relro = true;
+		}
+		if (p_headers[i].p_type == PT_DYNAMIC)
+		{
+			dyn_off = p_headers[i].p_offset;
+			dyn_size = p_headers[i].p_filesz;
+		}
+	}
+
+	if (dyn_off && dyn_size)
+	{
+		int n = dyn_size / sizeof(struct Elf32_Dyn);
+		struct Elf32_Dyn *dyns = malloc(dyn_size);
+		fseek(fp, dyn_off, SEEK_SET);
+		fread(dyns, sizeof(struct Elf32_Dyn), n, fp);
+
+		for (int i=0; i<n; i++)
+		{
+			// Has full RELRO?
+			if (dyns[i].d_tag == DT_BIND_NOW)
+			{
+				bind_now = true;
+				break;
+			}
+		}
+	}
+
 }
 
 void display_elf64(struct Elf64_Ehdr* header)
@@ -354,9 +448,11 @@ unsigned char read_elf_obj_size(FILE* fp)
 
 void display_sec_common()
 {
-	printf(" %s, ", nx ? "\x1b[32mNX enabled\x1b[0m" : "\x1b[31mNX disabled\x1b[0m");
+	printf("%s, ", nx ? "\x1b[32mNX enabled\x1b[0m" : "\x1b[31mNX disabled\x1b[0m");
 	printf("%s, ", pie ? "\x1b[32mPIE enabled\x1b[0m" : "\x1b[31mPIE disabled\x1b[0m");
-	printf("%s\n", canary ? "\x1b[32mStack canary enabled\x1b[0m" : "\x1b[31mStack canary disabled\x1b[0m");
+	printf("%s, ", canary ? "\x1b[32mStack canary enabled\x1b[0m" : "\x1b[31mStack canary disabled\x1b[0m");
+	printf("%s, ", relro && bind_now ? "\x1b[32mFull RELRO\x1b[0m" : relro ? "\x1b[33mPartial RELRO\x1b[0m" : "\x1b[31mNo RELRO\x1b[0m");
+	printf("%s\n", stripped ? "\x1b[32mStripped\x1b[0m" : "\x1b[31mNot stripped\x1b[0m");
 }
 
 int main(int argc, char* argv[])
@@ -408,7 +504,7 @@ int main(int argc, char* argv[])
 				printf("Failed to parse 32-bit ELF header\n");
 				return -EINVAL;
 			}
-			display_elf32(&elf32_header);
+			display_elf32(&elf32_header, elf_file);
 			check_sec32(&elf32_header, elf_file);
 			break;
 		case 0x02:

makefile

@@ -6,7 +6,7 @@ install:
 
 test:
 	make
-	gcc -m32 -fstack-protector main.c
+	gcc -m32 -fstack-protector -static -Wl,-z,relro,-z,now main.c
 	./helpelf a.out
 
 clean: