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Fix memory issues causing EXC_BAD_ACCESS
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Fix grabbed from PR facebook#84
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Pedro A Osuna committed Sep 24, 2021
1 parent 8ef82f0 commit fda9c70
Showing 1 changed file with 38 additions and 24 deletions.
62 changes: 38 additions & 24 deletions fishhook.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@
#include <mach-o/dyld.h>
#include <mach-o/loader.h>
#include <mach-o/nlist.h>
#include <pthread.h>

#ifdef __LP64__
typedef struct mach_header_64 mach_header_t;
Expand All @@ -54,13 +55,18 @@ typedef struct nlist nlist_t;
#define SEG_DATA_CONST "__DATA_CONST"
#endif

#ifndef SEG_AUTH_CONST
#define SEG_AUTH_CONST "__AUTH_CONST"
#endif

struct rebindings_entry {
struct rebinding *rebindings;
size_t rebindings_nel;
struct rebindings_entry *next;
};

static struct rebindings_entry *_rebindings_head;
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

static int prepend_rebindings(struct rebindings_entry **rebindings_head,
struct rebinding rebindings[],
Expand Down Expand Up @@ -90,7 +96,7 @@ static vm_prot_t get_protection(void *sectionStart) {
mach_msg_type_number_t count = VM_REGION_BASIC_INFO_COUNT_64;
vm_region_basic_info_data_64_t info;
kern_return_t info_ret = vm_region_64(
task, &address, &size, VM_REGION_BASIC_INFO_64, (vm_region_info_64_t)&info, &count, &object);
task, &address, &size, VM_REGION_BASIC_INFO_64, (vm_region_info_64_t)&info, &count, &object);
#else
mach_msg_type_number_t count = VM_REGION_BASIC_INFO_COUNT;
vm_region_basic_info_data_t info;
Expand All @@ -109,17 +115,23 @@ static void perform_rebinding_with_section(struct rebindings_entry *rebindings,
char *strtab,
uint32_t *indirect_symtab) {
const bool isDataConst = strcmp(section->segname, SEG_DATA_CONST) == 0;
const bool isAuthConst = strcmp(section->segname, SEG_AUTH_CONST) == 0;
uint32_t *indirect_symbol_indices = indirect_symtab + section->reserved1;
void **indirect_symbol_bindings = (void **)((uintptr_t)slide + section->addr);
vm_prot_t oldProtection = VM_PROT_READ;
if (isDataConst) {
oldProtection = get_protection(rebindings);
mprotect(indirect_symbol_bindings, section->size, PROT_READ | PROT_WRITE);
vm_size_t trunc_address = (vm_size_t)indirect_symbol_bindings;
vm_size_t trunc_size = 0;
if (isDataConst || isAuthConst) {
trunc_address = trunc_page((vm_size_t)indirect_symbol_bindings);
trunc_size =(vm_size_t)indirect_symbol_bindings -trunc_address;
pthread_mutex_lock(&mutex);
oldProtection = get_protection((void *)trunc_address);
mprotect((void *)trunc_address, section->size+trunc_size, PROT_READ | PROT_WRITE);
}
for (uint i = 0; i < section->size / sizeof(void *); i++) {
uint32_t symtab_index = indirect_symbol_indices[i];
if (symtab_index == INDIRECT_SYMBOL_ABS || symtab_index == INDIRECT_SYMBOL_LOCAL ||
symtab_index == (INDIRECT_SYMBOL_LOCAL | INDIRECT_SYMBOL_ABS)) {
symtab_index == (INDIRECT_SYMBOL_LOCAL | INDIRECT_SYMBOL_ABS)) {
continue;
}
uint32_t strtab_offset = symtab[symtab_index].n_un.n_strx;
Expand All @@ -142,7 +154,7 @@ static void perform_rebinding_with_section(struct rebindings_entry *rebindings,
}
symbol_loop:;
}
if (isDataConst) {
if (isDataConst || isAuthConst) {
int protection = 0;
if (oldProtection & VM_PROT_READ) {
protection |= PROT_READ;
Expand All @@ -153,7 +165,8 @@ static void perform_rebinding_with_section(struct rebindings_entry *rebindings,
if (oldProtection & VM_PROT_EXECUTE) {
protection |= PROT_EXEC;
}
mprotect(indirect_symbol_bindings, section->size, protection);
mprotect((void *)trunc_address, section->size+trunc_size, protection);
pthread_mutex_unlock(&mutex);
}
}

Expand All @@ -164,12 +177,12 @@ static void rebind_symbols_for_image(struct rebindings_entry *rebindings,
if (dladdr(header, &info) == 0) {
return;
}

segment_command_t *cur_seg_cmd;
segment_command_t *linkedit_segment = NULL;
struct symtab_command* symtab_cmd = NULL;
struct dysymtab_command* dysymtab_cmd = NULL;

uintptr_t cur = (uintptr_t)header + sizeof(mach_header_t);
for (uint i = 0; i < header->ncmds; i++, cur += cur_seg_cmd->cmdsize) {
cur_seg_cmd = (segment_command_t *)cur;
Expand All @@ -183,31 +196,32 @@ static void rebind_symbols_for_image(struct rebindings_entry *rebindings,
dysymtab_cmd = (struct dysymtab_command*)cur_seg_cmd;
}
}

if (!symtab_cmd || !dysymtab_cmd || !linkedit_segment ||
!dysymtab_cmd->nindirectsyms) {
return;
}

// Find base symbol/string table addresses
uintptr_t linkedit_base = (uintptr_t)slide + linkedit_segment->vmaddr - linkedit_segment->fileoff;
nlist_t *symtab = (nlist_t *)(linkedit_base + symtab_cmd->symoff);
char *strtab = (char *)(linkedit_base + symtab_cmd->stroff);

// Get indirect symbol table (array of uint32_t indices into symbol table)
uint32_t *indirect_symtab = (uint32_t *)(linkedit_base + dysymtab_cmd->indirectsymoff);

cur = (uintptr_t)header + sizeof(mach_header_t);
for (uint i = 0; i < header->ncmds; i++, cur += cur_seg_cmd->cmdsize) {
cur_seg_cmd = (segment_command_t *)cur;
if (cur_seg_cmd->cmd == LC_SEGMENT_ARCH_DEPENDENT) {
if (strcmp(cur_seg_cmd->segname, SEG_DATA) != 0 &&
strcmp(cur_seg_cmd->segname, SEG_DATA_CONST) != 0) {
strcmp(cur_seg_cmd->segname, SEG_DATA_CONST) != 0 &&
strcmp(cur_seg_cmd->segname, SEG_AUTH_CONST) != 0) {
continue;
}
for (uint j = 0; j < cur_seg_cmd->nsects; j++) {
section_t *sect =
(section_t *)(cur + sizeof(segment_command_t)) + j;
(section_t *)(cur + sizeof(segment_command_t)) + j;
if ((sect->flags & SECTION_TYPE) == S_LAZY_SYMBOL_POINTERS) {
perform_rebinding_with_section(rebindings, sect, slide, symtab, strtab, indirect_symtab);
}
Expand All @@ -221,21 +235,21 @@ static void rebind_symbols_for_image(struct rebindings_entry *rebindings,

static void _rebind_symbols_for_image(const struct mach_header *header,
intptr_t slide) {
rebind_symbols_for_image(_rebindings_head, header, slide);
rebind_symbols_for_image(_rebindings_head, header, slide);
}

int rebind_symbols_image(void *header,
intptr_t slide,
struct rebinding rebindings[],
size_t rebindings_nel) {
struct rebindings_entry *rebindings_head = NULL;
int retval = prepend_rebindings(&rebindings_head, rebindings, rebindings_nel);
rebind_symbols_for_image(rebindings_head, (const struct mach_header *) header, slide);
if (rebindings_head) {
free(rebindings_head->rebindings);
}
free(rebindings_head);
return retval;
struct rebindings_entry *rebindings_head = NULL;
int retval = prepend_rebindings(&rebindings_head, rebindings, rebindings_nel);
rebind_symbols_for_image(rebindings_head, (const struct mach_header *) header, slide);
if (rebindings_head) {
free(rebindings_head->rebindings);
}
free(rebindings_head);
return retval;
}

int rebind_symbols(struct rebinding rebindings[], size_t rebindings_nel) {
Expand Down

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