ЛР1 Аскаров Эмиль P3310

solution/src/util/header/elf.h

+#ifndef __ELF_UTIL__
+#define __ELF_UTIL__
+
+#include "elf.h"
+
+#include <asm-generic/errno-base.h>
+#include <elf.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+int8_t process_header(int32_t fd, Elf64_Ehdr *header);
+
+int8_t read_string_table(int32_t fd, Elf64_Ehdr *header, Elf64_Shdr *section);
+
+int8_t process_segments(int32_t fd, Elf64_Ehdr *header);
+
+int8_t find_section(int32_t fd,
+                    Elf64_Ehdr *header,
+                    Elf64_Shdr *string_table_section,
+                    char *target_name,
+                    Elf64_Shdr *section);
+
+#endif

solution/src/util/elf.c

+#include "header/elf.h"
+
+#define SET_RIGHTS(flags, rights, flag, right)                            \
+  if (((flags) & (flag)) == (flag)) {                                     \
+    (rights) |= (right);                                                  \
+  }
+
+int8_t process_header(int32_t fd, Elf64_Ehdr *header) {
+  if (header == 0) return EINVAL;
+  if (read(fd, header, sizeof(Elf64_Ehdr)) != sizeof(Elf64_Ehdr)) {
+    return EIO;
+  }
+  unsigned char *e_ident = header->e_ident;
+  if (
+      (e_ident[EI_MAG0] << 24) +
+      (e_ident[EI_MAG1] << 16) +
+      (e_ident[EI_MAG2] << 8) +
+      (e_ident[EI_MAG3]) !=
+      (ELFMAG0 << 24) +
+      (ELFMAG1 << 16) +
+      (ELFMAG2 << 8) +
+      ELFMAG3
+      ) {
+    return EINVAL;
+  }
+  return 0;
+}
+
+static int8_t process_segment(int32_t fd, Elf64_Phdr *segment) {
+  if (segment == 0) return EINVAL;
+  if (segment->p_type != PT_LOAD) return 0;
+
+  Elf64_Addr addr = segment->p_vaddr - segment->p_vaddr % getpagesize();
+  Elf64_Xword size = segment->p_memsz + segment->p_vaddr % getpagesize();
+  if (mmap((void *) addr, size, PROT_WRITE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0) // NOLINT
+      == MAP_FAILED) {
+    return EINVAL;
+  }
+
+  if (lseek(fd, (off_t) segment->p_offset, SEEK_SET) == -1) {
+    return EINVAL;
+  }
+
+  if (read(fd, (void *) segment->p_vaddr, segment->p_filesz) != segment->p_filesz) { // NOLINT
+    return EIO;
+  }
+
+  int rights = 0;
+
+  SET_RIGHTS(segment->p_flags, rights, PF_R, PROT_READ);
+  SET_RIGHTS(segment->p_flags, rights, PF_W, PROT_WRITE);
+  SET_RIGHTS(segment->p_flags, rights, PF_X, PROT_EXEC);
+
+  if (mprotect((void *) addr, size, rights) == -1) { // NOLINT
+    return EIO;
+  }
+
+  return 0;
+}
+
+static int8_t string_equals(char *a, char *b) {
+  char *target = b;
+  while (*target != '\0') {
+    if (*a != *target) {
+      return 0;
+    }
+    target++;
+    a++;
+  }
+  return (int8_t) (*a == '\0');
+}
+
+static int8_t match_section_name(int32_t fd, Elf64_Shdr *section, Elf64_Shdr *table_section, char *target_name) {
+  if (section == 0 || table_section == 0 || target_name == 0) return EINVAL;
+  if (lseek(fd, (off_t) (table_section->sh_offset + section->sh_name), SEEK_SET) == -1) {
+    return EINVAL;
+  }
+  char section_name[255];
+  section_name[0] = '\0';
+
+  if (read(fd, &section_name, sizeof(section_name)) == -1) {
+    return EINVAL;
+  }
+  if (!string_equals(section_name, target_name)) {
+    return -1;
+  }
+  if (section->sh_flags & SHF_EXECINSTR) {
+    return 0;
+  }
+  return EINVAL;
+}
+
+int8_t process_segments(int32_t fd, Elf64_Ehdr *header) {
+  for (int i = 0; i < header->e_phnum; ++i) {
+    if (lseek(fd, (off_t) (header->e_phoff + i * sizeof(Elf64_Phdr)), SEEK_SET) == -1) {
+      close(fd);
+      return EINVAL;
+    }
+    Elf64_Phdr segment;
+    if (read(fd, &segment, sizeof(Elf64_Phdr)) != sizeof(Elf64_Phdr)) {
+      close(fd);
+      return EIO;
+    }
+    int8_t result;
+    if ((result = process_segment(fd, &segment)) != 0) {
+      return result;
+    }
+  }
+  return 0;
+}
+
+int8_t read_string_table(int32_t fd, Elf64_Ehdr *header, Elf64_Shdr *section) {
+  if (lseek(fd, (off_t) (header->e_shoff + header->e_shstrndx * sizeof(Elf64_Shdr)), SEEK_SET) == -1) {
+    close(fd);
+    return EINVAL;
+  }
+  if (read(fd, section, sizeof(Elf64_Shdr)) != sizeof(Elf64_Shdr)) {
+    close(fd);
+    return EIO;
+  }
+  return 0;
+}
+
+int8_t find_section(int32_t fd,
+                    Elf64_Ehdr *header,
+                    Elf64_Shdr *string_table_section,
+                    char *target_name,
+                    Elf64_Shdr *section) {
+  for (int i = 0; i < header->e_shnum; ++i) {
+    if (lseek(fd, (off_t) (header->e_shoff + i * sizeof(Elf64_Shdr)), SEEK_SET) == -1) {
+      return EINVAL;
+    }
+
+    if (read(fd, section, sizeof(Elf64_Shdr)) != sizeof(Elf64_Shdr)) {
+      return EIO;
+    }
+
+    int8_t result = match_section_name(fd, section, string_table_section, target_name);
+    if (result == 0) {
+      return 0;
+    } else if (result == -1) {
+      continue;
+    } else {
+      return result;
+    }
+  }
+  return EINVAL;
+}

solution/src/main.c

-#include <stdio.h>
+#include "util/header/elf.h"
 
-int main( int argc, char** argv ) {
-    (void) argc; (void) argv; // supress 'unused parameters' warning
+#include <asm-generic/errno-base.h>
+#include <fcntl.h>
 
-    return 0;
+int main(int argc, char **argv) {
+  if (argc != 3) return EINVAL;
+  int32_t fd = open(argv[1], O_RDONLY);
+  if (fd == -1) {
+    close(fd);
+    return ENOENT;
+  }
+  Elf64_Ehdr header;
+  int8_t result;
+  if ((result = process_header(fd, &header)) != 0) {
+    close(fd);
+    return result;
+  }
+  if ((result = process_segments(fd, &header)) != 0) {
+    close(fd);
+    return result;
+  }
+  Elf64_Shdr string_table_section;
+  if ((result = read_string_table(fd, &header, &string_table_section)) != 0) {
+    close(fd);
+    return result;
+  }
+
+  Elf64_Shdr section;
+  result = find_section(fd, &header, &string_table_section, argv[2], &section);
+  if (result != 0) {
+    close(fd);
+    return result;
+  }
+
+  ((void(*)(void)) section.sh_addr)(); // NOLINT
+  close(fd);
+  return 0;
 }

[Andrey Zhdanov]

принято без защиты