kernel/ptrace.c

   1 /*
   2  * linux/kernel/ptrace.c
   3  *
   4  * (C) Copyright 1999 Linus Torvalds
   5  *
   6  * Common interfaces for "ptrace()" which we do not want
   7  * to continually duplicate across every architecture.
   8  */
   9
  10 #include <linux/capability.h>
  11 #include <linux/module.h>
  12 #include <linux/sched.h>
  13 #include <linux/errno.h>
  14 #include <linux/mm.h>
  15 #include <linux/highmem.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/smp_lock.h>
  18 #include <linux/ptrace.h>
  19 #include <linux/security.h>
  20 #include <linux/signal.h>
  21
  22 #include <asm/pgtable.h>
  23 #include <asm/uaccess.h>
  24
  25 /*
  26  * ptrace a task: make the debugger its new parent and
  27  * move it to the ptrace list.
  28  *
  29  * Must be called with the tasklist lock write-held.
  30  */
  31 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
  32 {
  33         BUG_ON(!list_empty(&child->ptrace_list));
  34         if (child->parent == new_parent)
  35                 return;
  36         list_add(&child->ptrace_list, &child->parent->ptrace_children);
  37         remove_parent(child);
  38         child->parent = new_parent;
  39         add_parent(child);
  40 }
  41
  42 /*
  43  * Turn a tracing stop into a normal stop now, since with no tracer there
  44  * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
  45  * signal sent that would resume the child, but didn't because it was in
  46  * TASK_TRACED, resume it now.
  47  * Requires that irqs be disabled.
  48  */
  49 void ptrace_untrace(struct task_struct *child)
  50 {
  51         spin_lock(&child->sighand->siglock);
  52         if (child->state == TASK_TRACED) {
  53                 if (child->signal->flags & SIGNAL_STOP_STOPPED) {
  54                         child->state = TASK_STOPPED;
  55                 } else {
  56                         signal_wake_up(child, 1);
  57                 }
  58         }
  59         spin_unlock(&child->sighand->siglock);
  60 }
  61
  62 /*
  63  * unptrace a task: move it back to its original parent and
  64  * remove it from the ptrace list.
  65  *
  66  * Must be called with the tasklist lock write-held.
  67  */
  68 void __ptrace_unlink(struct task_struct *child)
  69 {
  70         BUG_ON(!child->ptrace);
  71
  72         child->ptrace = 0;
  73         if (!list_empty(&child->ptrace_list)) {
  74                 list_del_init(&child->ptrace_list);
  75                 remove_parent(child);
  76                 child->parent = child->real_parent;
  77                 add_parent(child);
  78         }
  79
  80         if (child->state == TASK_TRACED)
  81                 ptrace_untrace(child);
  82 }
  83
  84 /*
  85  * Check that we have indeed attached to the thing..
  86  */
  87 int ptrace_check_attach(struct task_struct *child, int kill)
  88 {
  89         int ret = -ESRCH;
  90
  91         /*
  92          * We take the read lock around doing both checks to close a
  93          * possible race where someone else was tracing our child and
  94          * detached between these two checks.  After this locked check,
  95          * we are sure that this is our traced child and that can only
  96          * be changed by us so it's not changing right after this.
  97          */
  98         read_lock(&tasklist_lock);
  99         if ((child->ptrace & PT_PTRACED) && child->parent == current &&
 100             (!(child->ptrace & PT_ATTACHED) || child->real_parent != current)
 101             && child->signal != NULL) {
 102                 ret = 0;
 103                 spin_lock_irq(&child->sighand->siglock);
 104                 if (child->state == TASK_STOPPED) {
 105                         child->state = TASK_TRACED;
 106                 } else if (child->state != TASK_TRACED && !kill) {
 107                         ret = -ESRCH;
 108                 }
 109                 spin_unlock_irq(&child->sighand->siglock);
 110         }
 111         read_unlock(&tasklist_lock);
 112
 113         if (!ret && !kill) {
 114                 wait_task_inactive(child);
 115         }
 116
 117         /* All systems go.. */
 118         return ret;
 119 }
 120
 121 static int may_attach(struct task_struct *task)
 122 {
 123         /* May we inspect the given task?
 124          * This check is used both for attaching with ptrace
 125          * and for allowing access to sensitive information in /proc.
 126          *
 127          * ptrace_attach denies several cases that /proc allows
 128          * because setting up the necessary parent/child relationship
 129          * or halting the specified task is impossible.
 130          */
 131         int dumpable = 0;
 132         /* Don't let security modules deny introspection */
 133         if (task == current)
 134                 return 0;
 135         if (((current->uid != task->euid) ||
 136              (current->uid != task->suid) ||
 137              (current->uid != task->uid) ||
 138              (current->gid != task->egid) ||
 139              (current->gid != task->sgid) ||
 140              (current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
 141                 return -EPERM;
 142         smp_rmb();
 143         if (task->mm)
 144                 dumpable = task->mm->dumpable;
 145         if (!dumpable && !capable(CAP_SYS_PTRACE))
 146                 return -EPERM;
 147
 148         return security_ptrace(current, task);
 149 }
 150
 151 int ptrace_may_attach(struct task_struct *task)
 152 {
 153         int err;
 154         task_lock(task);
 155         err = may_attach(task);
 156         task_unlock(task);
 157         return !err;
 158 }
 159
 160 int ptrace_attach(struct task_struct *task)
 161 {
 162         int retval;
 163
 164         retval = -EPERM;
 165         if (task->pid <= 1)
 166                 goto out;
 167         if (task->tgid == current->tgid)
 168                 goto out;
 169
 170 repeat:
 171         /*
 172          * Nasty, nasty.
 173          *
 174          * We want to hold both the task-lock and the
 175          * tasklist_lock for writing at the same time.
 176          * But that's against the rules (tasklist_lock
 177          * is taken for reading by interrupts on other
 178          * cpu's that may have task_lock).
 179          */
 180         task_lock(task);
 181         local_irq_disable();
 182         if (!write_trylock(&tasklist_lock)) {
 183                 local_irq_enable();
 184                 task_unlock(task);
 185                 do {
 186                         cpu_relax();
 187                 } while (!write_can_lock(&tasklist_lock));
 188                 goto repeat;
 189         }
 190
 191         if (!task->mm)
 192                 goto bad;
 193         /* the same process cannot be attached many times */
 194         if (task->ptrace & PT_PTRACED)
 195                 goto bad;
 196         retval = may_attach(task);
 197         if (retval)
 198                 goto bad;
 199
 200         /* Go */
 201         task->ptrace |= PT_PTRACED | ((task->real_parent != current)
 202                                       ? PT_ATTACHED : 0);
 203         if (capable(CAP_SYS_PTRACE))
 204                 task->ptrace |= PT_PTRACE_CAP;
 205
 206         __ptrace_link(task, current);
 207
 208         force_sig_specific(SIGSTOP, task);
 209
 210 bad:
 211         write_unlock_irq(&tasklist_lock);
 212         task_unlock(task);
 213 out:
 214         return retval;
 215 }
 216
 217 static inline void __ptrace_detach(struct task_struct *child, unsigned int data)
 218 {
 219         child->exit_code = data;
 220         /* .. re-parent .. */
 221         __ptrace_unlink(child);
 222         /* .. and wake it up. */
 223         if (child->exit_state != EXIT_ZOMBIE)
 224                 wake_up_process(child);
 225 }
 226
 227 int ptrace_detach(struct task_struct *child, unsigned int data)
 228 {
 229         if (!valid_signal(data))
 230                 return -EIO;
 231
 232         /* Architecture-specific hardware disable .. */
 233         ptrace_disable(child);
 234
 235         write_lock_irq(&tasklist_lock);
 236         /* protect against de_thread()->release_task() */
 237         if (child->ptrace)
 238                 __ptrace_detach(child, data);
 239         write_unlock_irq(&tasklist_lock);
 240
 241         return 0;
 242 }
 243
 244 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
 245 {
 246         int copied = 0;
 247
 248         while (len > 0) {
 249                 char buf[128];
 250                 int this_len, retval;
 251
 252                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 253                 retval = access_process_vm(tsk, src, buf, this_len, 0);
 254                 if (!retval) {
 255                         if (copied)
 256                                 break;
 257                         return -EIO;
 258                 }
 259                 if (copy_to_user(dst, buf, retval))
 260                         return -EFAULT;
 261                 copied += retval;
 262                 src += retval;
 263                 dst += retval;
 264                 len -= retval;
 265         }
 266         return copied;
 267 }
 268
 269 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
 270 {
 271         int copied = 0;
 272
 273         while (len > 0) {
 274                 char buf[128];
 275                 int this_len, retval;
 276
 277                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 278                 if (copy_from_user(buf, src, this_len))
 279                         return -EFAULT;
 280                 retval = access_process_vm(tsk, dst, buf, this_len, 1);
 281                 if (!retval) {
 282                         if (copied)
 283                                 break;
 284                         return -EIO;
 285                 }
 286                 copied += retval;
 287                 src += retval;
 288                 dst += retval;
 289                 len -= retval;
 290         }
 291         return copied;
 292 }
 293
 294 static int ptrace_setoptions(struct task_struct *child, long data)
 295 {
 296         child->ptrace &= ~PT_TRACE_MASK;
 297
 298         if (data & PTRACE_O_TRACESYSGOOD)
 299                 child->ptrace |= PT_TRACESYSGOOD;
 300
 301         if (data & PTRACE_O_TRACEFORK)
 302                 child->ptrace |= PT_TRACE_FORK;
 303
 304         if (data & PTRACE_O_TRACEVFORK)
 305                 child->ptrace |= PT_TRACE_VFORK;
 306
 307         if (data & PTRACE_O_TRACECLONE)
 308                 child->ptrace |= PT_TRACE_CLONE;
 309
 310         if (data & PTRACE_O_TRACEEXEC)
 311                 child->ptrace |= PT_TRACE_EXEC;
 312
 313         if (data & PTRACE_O_TRACEVFORKDONE)
 314                 child->ptrace |= PT_TRACE_VFORK_DONE;
 315
 316         if (data & PTRACE_O_TRACEEXIT)
 317                 child->ptrace |= PT_TRACE_EXIT;
 318
 319         return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
 320 }
 321
 322 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t __user * data)
 323 {
 324         siginfo_t lastinfo;
 325         int error = -ESRCH;
 326
 327         read_lock(&tasklist_lock);
 328         if (likely(child->sighand != NULL)) {
 329                 error = -EINVAL;
 330                 spin_lock_irq(&child->sighand->siglock);
 331                 if (likely(child->last_siginfo != NULL)) {
 332                         lastinfo = *child->last_siginfo;
 333                         error = 0;
 334                 }
 335                 spin_unlock_irq(&child->sighand->siglock);
 336         }
 337         read_unlock(&tasklist_lock);
 338         if (!error)
 339                 return copy_siginfo_to_user(data, &lastinfo);
 340         return error;
 341 }
 342
 343 static int ptrace_setsiginfo(struct task_struct *child, siginfo_t __user * data)
 344 {
 345         siginfo_t newinfo;
 346         int error = -ESRCH;
 347
 348         if (copy_from_user(&newinfo, data, sizeof (siginfo_t)))
 349                 return -EFAULT;
 350
 351         read_lock(&tasklist_lock);
 352         if (likely(child->sighand != NULL)) {
 353                 error = -EINVAL;
 354                 spin_lock_irq(&child->sighand->siglock);
 355                 if (likely(child->last_siginfo != NULL)) {
 356                         *child->last_siginfo = newinfo;
 357                         error = 0;
 358                 }
 359                 spin_unlock_irq(&child->sighand->siglock);
 360         }
 361         read_unlock(&tasklist_lock);
 362         return error;
 363 }
 364
 365 int ptrace_request(struct task_struct *child, long request,
 366                    long addr, long data)
 367 {
 368         int ret = -EIO;
 369
 370         switch (request) {
 371 #ifdef PTRACE_OLDSETOPTIONS
 372         case PTRACE_OLDSETOPTIONS:
 373 #endif
 374         case PTRACE_SETOPTIONS:
 375                 ret = ptrace_setoptions(child, data);
 376                 break;
 377         case PTRACE_GETEVENTMSG:
 378                 ret = put_user(child->ptrace_message, (unsigned long __user *) data);
 379                 break;
 380         case PTRACE_GETSIGINFO:
 381                 ret = ptrace_getsiginfo(child, (siginfo_t __user *) data);
 382                 break;
 383         case PTRACE_SETSIGINFO:
 384                 ret = ptrace_setsiginfo(child, (siginfo_t __user *) data);
 385                 break;
 386         default:
 387                 break;
 388         }
 389
 390         return ret;
 391 }
 392
 393 /**
 394  * ptrace_traceme  --  helper for PTRACE_TRACEME
 395  *
 396  * Performs checks and sets PT_PTRACED.
 397  * Should be used by all ptrace implementations for PTRACE_TRACEME.
 398  */
 399 int ptrace_traceme(void)
 400 {
 401         int ret = -EPERM;
 402
 403         /*
 404          * Are we already being traced?
 405          */
 406         task_lock(current);
 407         if (!(current->ptrace & PT_PTRACED)) {
 408                 ret = security_ptrace(current->parent, current);
 409                 /*
 410                  * Set the ptrace bit in the process ptrace flags.
 411                  */
 412                 if (!ret)
 413                         current->ptrace |= PT_PTRACED;
 414         }
 415         task_unlock(current);
 416         return ret;
 417 }
 418
 419 /**
 420  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
 421  * @pid:       process id to grab a task_struct reference of
 422  *
 423  * This function is a helper for ptrace implementations.  It checks
 424  * permissions and then grabs a task struct for use of the actual
 425  * ptrace implementation.
 426  *
 427  * Returns the task_struct for @pid or an ERR_PTR() on failure.
 428  */
 429 struct task_struct *ptrace_get_task_struct(pid_t pid)
 430 {
 431         struct task_struct *child;
 432
 433         /*
 434          * Tracing init is not allowed.
 435          */
 436         if (pid == 1)
 437                 return ERR_PTR(-EPERM);
 438
 439         read_lock(&tasklist_lock);
 440         child = find_task_by_pid(pid);
 441         if (child)
 442                 get_task_struct(child);
 443         read_unlock(&tasklist_lock);
 444         if (!child)
 445                 return ERR_PTR(-ESRCH);
 446         return child;
 447 }
 448
 449 #ifndef __ARCH_SYS_PTRACE
 450 asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
 451 {
 452         struct task_struct *child;
 453         long ret;
 454
 455         /*
 456          * This lock_kernel fixes a subtle race with suid exec
 457          */
 458         lock_kernel();
 459         if (request == PTRACE_TRACEME) {
 460                 ret = ptrace_traceme();
 461                 goto out;
 462         }
 463
 464         child = ptrace_get_task_struct(pid);
 465         if (IS_ERR(child)) {
 466                 ret = PTR_ERR(child);
 467                 goto out;
 468         }
 469
 470         if (request == PTRACE_ATTACH) {
 471                 ret = ptrace_attach(child);
 472                 goto out_put_task_struct;
 473         }
 474
 475         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 476         if (ret < 0)
 477                 goto out_put_task_struct;
 478
 479         ret = arch_ptrace(child, request, addr, data);
 480         if (ret < 0)
 481                 goto out_put_task_struct;
 482
 483  out_put_task_struct:
 484         put_task_struct(child);
 485  out:
 486         unlock_kernel();
 487         return ret;
 488 }
 489 #endif /* __ARCH_SYS_PTRACE */