root/fs/exec.c

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DEFINITIONS

This source file includes following definitions.
  1. core_dump
  2. sys_uselib
  3. create_tables
  4. count
  5. copy_strings
  6. change_ldt
  7. read_omagic
  8. do_execve

   1 /*
   2  *  linux/fs/exec.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6 
   7 /*
   8  * #!-checking implemented by tytso.
   9  */
  10 
  11 /*
  12  * Demand-loading implemented 01.12.91 - no need to read anything but
  13  * the header into memory. The inode of the executable is put into
  14  * "current->executable", and page faults do the actual loading. Clean.
  15  *
  16  * Once more I can proudly say that linux stood up to being changed: it
  17  * was less than 2 hours work to get demand-loading completely implemented.
  18  */
  19 
  20 #include <linux/fs.h>
  21 #include <linux/sched.h>
  22 #include <linux/kernel.h>
  23 #include <linux/mm.h>
  24 #include <linux/a.out.h>
  25 #include <linux/errno.h>
  26 #include <linux/signal.h>
  27 #include <linux/string.h>
  28 #include <linux/stat.h>
  29 #include <linux/fcntl.h>
  30 #include <linux/ptrace.h>
  31 #include <linux/user.h>
  32 
  33 #include <asm/segment.h>
  34 
  35 extern int sys_exit(int exit_code);
  36 extern int sys_close(int fd);
  37 
  38 /*
  39  * MAX_ARG_PAGES defines the number of pages allocated for arguments
  40  * and envelope for the new program. 32 should suffice, this gives
  41  * a maximum env+arg of 128kB !
  42  */
  43 #define MAX_ARG_PAGES 32
  44 
  45 /*
  46  * These are the only things you should do on a core-file: use only these
  47  * macros to write out all the necessary info.
  48  */
  49 #define DUMP_WRITE(addr,nr) \
  50 while (file.f_op->write(inode,&file,(char *)(addr),(nr)) != (nr)) goto close_coredump
  51 
  52 #define DUMP_SEEK(offset) \
  53 if (file.f_op->lseek) { \
  54         if (file.f_op->lseek(inode,&file,(offset),0) != (offset)) \
  55                 goto close_coredump; \
  56 } else file.f_pos = (offset)            
  57 
  58 /*
  59  * Routine writes a core dump image in the current directory.
  60  * Currently only a stub-function.
  61  *
  62  * Note that setuid/setgid files won't make a core-dump if the uid/gid
  63  * changed due to the set[u|g]id. It's enforced by the "current->dumpable"
  64  * field, which also makes sure the core-dumps won't be recursive if the
  65  * dumping of the process results in another error..
  66  */
  67 int core_dump(long signr, struct pt_regs * regs)
     /* [previous][next][first][last][top][bottom][index][help] */
  68 {
  69         struct inode * inode = NULL;
  70         struct file file;
  71         unsigned short fs;
  72         int has_dumped = 0;
  73         register int dump_start, dump_size;
  74         struct user dump;
  75 
  76         if (!current->dumpable)
  77                 return 0;
  78         current->dumpable = 0;
  79 /* See if we have enough room to write the upage.  */
  80         if(current->rlim[RLIMIT_CORE].rlim_cur < PAGE_SIZE/1024) return 0;
  81         __asm__("mov %%fs,%0":"=r" (fs));
  82         __asm__("mov %0,%%fs"::"r" ((unsigned short) 0x10));
  83         if (open_namei("core",O_CREAT | O_WRONLY | O_TRUNC,0600,&inode,NULL)) {
  84                 inode = NULL;
  85                 goto end_coredump;
  86         }
  87         if (!S_ISREG(inode->i_mode))
  88                 goto end_coredump;
  89         if (!inode->i_op || !inode->i_op->default_file_ops)
  90                 goto end_coredump;
  91         file.f_mode = 3;
  92         file.f_flags = 0;
  93         file.f_count = 1;
  94         file.f_inode = inode;
  95         file.f_pos = 0;
  96         file.f_reada = 0;
  97         file.f_op = inode->i_op->default_file_ops;
  98         if (file.f_op->open)
  99                 if (file.f_op->open(inode,&file))
 100                         goto end_coredump;
 101         if (!file.f_op->write)
 102                 goto close_coredump;
 103         has_dumped = 1;
 104 /* changed the size calculations - should hopefully work better. lbt */
 105         dump.magic = CMAGIC;
 106         dump.start_code = 0;
 107         dump.start_stack = regs->esp & ~(PAGE_SIZE - 1);
 108         dump.u_tsize = ((unsigned long) current->end_code) >> 12;
 109         dump.u_dsize = ((unsigned long) (current->brk + (PAGE_SIZE-1))) >> 12;
 110         dump.u_dsize -= dump.u_tsize;
 111         dump.u_ssize = 0;
 112         if (dump.start_stack < TASK_SIZE)
 113                 dump.u_ssize = ((unsigned long) (TASK_SIZE - dump.start_stack)) >> 12;
 114 /* If the size of the dump file exceeds the rlimit, then see what would happen
 115    if we wrote the stack, but not the data area.  */
 116         if ((dump.u_dsize+dump.u_ssize+1) * PAGE_SIZE/1024 >
 117             current->rlim[RLIMIT_CORE].rlim_cur)
 118                 dump.u_dsize = 0;
 119 /* Make sure we have enough room to write the stack and data areas. */
 120         if ((dump.u_ssize+1) * PAGE_SIZE / 1024 >
 121             current->rlim[RLIMIT_CORE].rlim_cur)
 122                 dump.u_ssize = 0;
 123         dump.u_comm = 0;
 124         dump.u_ar0 = (struct pt_regs *)(((int)(&dump.regs)) -((int)(&dump)));
 125         dump.signal = signr;
 126         dump.regs = *regs;
 127 /* Flag indicating the math stuff is valid. */
 128         if (dump.u_fpvalid = current->used_math) {
 129                 if (last_task_used_math == current)
 130                         __asm__("clts ; fnsave %0"::"m" (dump.i387));
 131                 else
 132                         memcpy(&dump.i387,&current->tss.i387,sizeof(dump.i387));
 133         };
 134         __asm__("mov %0,%%fs"::"r" ((unsigned short) 0x10));
 135         DUMP_WRITE(&dump,sizeof(dump));
 136         DUMP_SEEK(sizeof(dump));
 137  /* Dump the task struct.  Not be used by gdb, but could be useful */
 138         DUMP_WRITE(current,sizeof(*current));
 139 /* Now dump all of the user data.  Include malloced stuff as well */
 140         DUMP_SEEK(PAGE_SIZE);
 141 /* now we start writing out the user space info */
 142         __asm__("mov %0,%%fs"::"r" ((unsigned short) 0x17));
 143 /* Dump the data area */
 144         if (dump.u_dsize != 0) {
 145                 dump_start = dump.u_tsize << 12;
 146                 dump_size = dump.u_dsize << 12;
 147                 DUMP_WRITE(dump_start,dump_size);
 148         };
 149 /* Now prepare to dump the stack area */
 150         if (dump.u_ssize != 0) {
 151                 dump_start = dump.start_stack;
 152                 dump_size = dump.u_ssize << 12;
 153                 DUMP_WRITE(dump_start,dump_size);
 154         };
 155 close_coredump:
 156         if (file.f_op->release)
 157                 file.f_op->release(inode,&file);
 158 end_coredump:
 159         __asm__("mov %0,%%fs"::"r" (fs));
 160         iput(inode);
 161         return has_dumped;
 162 }
 163 
 164 /*
 165  * Note that a shared library must be both readable and executable due to
 166  * security reasons.
 167  *
 168  * Also note that we take the address to load from from the file itself.
 169  */
 170 int sys_uselib(const char * library)
     /* [previous][next][first][last][top][bottom][index][help] */
 171 {
 172 #define libnum  (current->numlibraries)
 173         struct inode * inode;
 174         struct buffer_head * bh;
 175         struct exec ex;
 176         int error;
 177 
 178         if (!library || get_limit(0x17) != TASK_SIZE)
 179                 return -EINVAL;
 180         if ((libnum >= MAX_SHARED_LIBS) || (libnum < 0))
 181                 return -EINVAL;
 182         error = namei(library,&inode);
 183         if (error)
 184                 return error;
 185         if (!inode->i_sb || !S_ISREG(inode->i_mode) || !permission(inode,MAY_READ)) {
 186                 iput(inode);
 187                 return -EACCES;
 188         }
 189         if (!(bh = bread(inode->i_dev,bmap(inode,0),inode->i_sb->s_blocksize))) {
 190                 iput(inode);
 191                 return -EACCES;
 192         }
 193         if (!IS_RDONLY(inode)) {
 194                 inode->i_atime = CURRENT_TIME;
 195                 inode->i_dirt = 1;
 196         }
 197         ex = *(struct exec *) bh->b_data;
 198         brelse(bh);
 199         if (N_MAGIC(ex) != ZMAGIC || ex.a_trsize || ex.a_drsize ||
 200                 ex.a_text+ex.a_data+ex.a_bss>0x3000000 ||
 201                 inode->i_size < ex.a_text+ex.a_data+ex.a_syms+N_TXTOFF(ex)) {
 202                 iput(inode);
 203                 return -ENOEXEC;
 204         }
 205         current->libraries[libnum].library = inode;
 206         current->libraries[libnum].start = ex.a_entry;
 207         current->libraries[libnum].length = (ex.a_data+ex.a_text+0xfff) & 0xfffff000;
 208         current->libraries[libnum].bss = (ex.a_bss+0xfff) & 0xfffff000;
 209 #if 0
 210         printk("Loaded library %d at %08x, length %08x\n",
 211                 libnum,
 212                 current->libraries[libnum].start,
 213                 current->libraries[libnum].length);
 214 #endif
 215         libnum++;
 216         return 0;
 217 #undef libnum
 218 }
 219 
 220 /*
 221  * create_tables() parses the env- and arg-strings in new user
 222  * memory and creates the pointer tables from them, and puts their
 223  * addresses on the "stack", returning the new stack pointer value.
 224  */
 225 static unsigned long * create_tables(char * p,int argc,int envc)
     /* [previous][next][first][last][top][bottom][index][help] */
 226 {
 227         unsigned long *argv,*envp;
 228         unsigned long * sp;
 229 
 230         sp = (unsigned long *) (0xfffffffc & (unsigned long) p);
 231         sp -= envc+1;
 232         envp = sp;
 233         sp -= argc+1;
 234         argv = sp;
 235         put_fs_long((unsigned long)envp,--sp);
 236         put_fs_long((unsigned long)argv,--sp);
 237         put_fs_long((unsigned long)argc,--sp);
 238         while (argc-->0) {
 239                 put_fs_long((unsigned long) p,argv++);
 240                 while (get_fs_byte(p++)) /* nothing */ ;
 241         }
 242         put_fs_long(0,argv);
 243         while (envc-->0) {
 244                 put_fs_long((unsigned long) p,envp++);
 245                 while (get_fs_byte(p++)) /* nothing */ ;
 246         }
 247         put_fs_long(0,envp);
 248         return sp;
 249 }
 250 
 251 /*
 252  * count() counts the number of arguments/envelopes
 253  */
 254 static int count(char ** argv)
     /* [previous][next][first][last][top][bottom][index][help] */
 255 {
 256         int i=0;
 257         char ** tmp;
 258 
 259         if (tmp = argv)
 260                 while (get_fs_long((unsigned long *) (tmp++)))
 261                         i++;
 262 
 263         return i;
 264 }
 265 
 266 /*
 267  * 'copy_string()' copies argument/envelope strings from user
 268  * memory to free pages in kernel mem. These are in a format ready
 269  * to be put directly into the top of new user memory.
 270  *
 271  * Modified by TYT, 11/24/91 to add the from_kmem argument, which specifies
 272  * whether the string and the string array are from user or kernel segments:
 273  * 
 274  * from_kmem     argv *        argv **
 275  *    0          user space    user space
 276  *    1          kernel space  user space
 277  *    2          kernel space  kernel space
 278  * 
 279  * We do this by playing games with the fs segment register.  Since it
 280  * it is expensive to load a segment register, we try to avoid calling
 281  * set_fs() unless we absolutely have to.
 282  */
 283 static unsigned long copy_strings(int argc,char ** argv,unsigned long *page,
     /* [previous][next][first][last][top][bottom][index][help] */
 284                 unsigned long p, int from_kmem)
 285 {
 286         char *tmp, *pag = NULL;
 287         int len, offset = 0;
 288         unsigned long old_fs, new_fs;
 289 
 290         if (!p)
 291                 return 0;       /* bullet-proofing */
 292         new_fs = get_ds();
 293         old_fs = get_fs();
 294         if (from_kmem==2)
 295                 set_fs(new_fs);
 296         while (argc-- > 0) {
 297                 if (from_kmem == 1)
 298                         set_fs(new_fs);
 299                 if (!(tmp = (char *)get_fs_long(((unsigned long *)argv)+argc)))
 300                         panic("argc is wrong");
 301                 if (from_kmem == 1)
 302                         set_fs(old_fs);
 303                 len=0;          /* remember zero-padding */
 304                 do {
 305                         len++;
 306                 } while (get_fs_byte(tmp++));
 307                 if (p < len) {  /* this shouldn't happen - 128kB */
 308                         set_fs(old_fs);
 309                         return 0;
 310                 }
 311                 while (len) {
 312                         --p; --tmp; --len;
 313                         if (--offset < 0) {
 314                                 offset = p % PAGE_SIZE;
 315                                 if (from_kmem==2)
 316                                         set_fs(old_fs);
 317                                 if (!(pag = (char *) page[p/PAGE_SIZE]) &&
 318                                     !(pag = (char *) page[p/PAGE_SIZE] =
 319                                       (unsigned long *) get_free_page(GFP_USER))) 
 320                                         return 0;
 321                                 if (from_kmem==2)
 322                                         set_fs(new_fs);
 323 
 324                         }
 325                         *(pag + offset) = get_fs_byte(tmp);
 326                 }
 327         }
 328         if (from_kmem==2)
 329                 set_fs(old_fs);
 330         return p;
 331 }
 332 
 333 static unsigned long change_ldt(unsigned long text_size,unsigned long * page)
     /* [previous][next][first][last][top][bottom][index][help] */
 334 {
 335         unsigned long code_limit,data_limit,code_base,data_base;
 336         int i;
 337 
 338         code_limit = TASK_SIZE;
 339         data_limit = TASK_SIZE;
 340         code_base = data_base = 0;
 341         current->start_code = code_base;
 342         set_base(current->ldt[1],code_base);
 343         set_limit(current->ldt[1],code_limit);
 344         set_base(current->ldt[2],data_base);
 345         set_limit(current->ldt[2],data_limit);
 346 /* make sure fs points to the NEW data segment */
 347         __asm__("pushl $0x17\n\tpop %%fs"::);
 348         data_base += data_limit;
 349         for (i=MAX_ARG_PAGES-1 ; i>=0 ; i--) {
 350                 data_base -= PAGE_SIZE;
 351                 if (page[i])
 352                         put_dirty_page(current,page[i],data_base);
 353         }
 354         return data_limit;
 355 }
 356 
 357 static void read_omagic(struct inode *inode, int bytes)
     /* [previous][next][first][last][top][bottom][index][help] */
 358 {
 359         struct buffer_head *bh;
 360         int n, blkno, blk = 0;
 361         char *dest = (char *) 0;
 362         unsigned int block_size;
 363 
 364         block_size = 1024;
 365         if (inode->i_sb)
 366                 block_size = inode->i_sb->s_blocksize;
 367         while (bytes > 0) {
 368                 if (!(blkno = bmap(inode, blk)))
 369                         sys_exit(-1);
 370                 if (!(bh = bread(inode->i_dev, blkno, block_size)))
 371                         sys_exit(-1);
 372                 n = (blk ? block_size : block_size - sizeof(struct exec));
 373                 if (bytes < n)
 374                         n = bytes;
 375 
 376                 memcpy_tofs(dest, (blk ? bh->b_data :
 377                                 bh->b_data + sizeof(struct exec)), n);
 378                 brelse(bh);
 379                 ++blk;
 380                 dest += n;
 381                 bytes -= n;
 382         }
 383         iput(inode);
 384         current->executable = NULL;
 385 }
 386 
 387 /*
 388  * 'do_execve()' executes a new program.
 389  *
 390  * NOTE! We leave 4MB free at the top of the data-area for a loadable
 391  * library.
 392  */
 393 int do_execve(unsigned long * eip,long tmp,char * filename,
     /* [previous][next][first][last][top][bottom][index][help] */
 394         char ** argv, char ** envp)
 395 {
 396         struct inode * inode;
 397         struct buffer_head * bh;
 398         struct exec ex;
 399         unsigned long page[MAX_ARG_PAGES];
 400         int i,argc,envc;
 401         int e_uid, e_gid;
 402         int retval;
 403         int sh_bang = 0;
 404         unsigned long p=PAGE_SIZE*MAX_ARG_PAGES-4;
 405         int ch;
 406 
 407         if ((0xffff & eip[1]) != 0x000f)
 408                 panic("execve called from supervisor mode");
 409         for (i=0 ; i<MAX_ARG_PAGES ; i++)       /* clear page-table */
 410                 page[i]=0;
 411         retval = namei(filename,&inode);        /* get executable inode */
 412         if (retval)
 413                 return retval;
 414         argc = count(argv);
 415         envc = count(envp);
 416         
 417 restart_interp:
 418         if (!S_ISREG(inode->i_mode)) {  /* must be regular file */
 419                 retval = -EACCES;
 420                 goto exec_error2;
 421         }
 422         if (IS_NOEXEC(inode)) {         /* FS mustn't be mounted noexec */
 423                 retval = -EPERM;
 424                 goto exec_error2;
 425         }
 426         if (!inode->i_sb) {
 427                 retval = -EACCES;
 428                 goto exec_error2;
 429         }
 430         i = inode->i_mode;
 431         if (IS_NOSUID(inode) && (((i & S_ISUID) && inode->i_uid != current->
 432             euid) || ((i & S_ISGID) && inode->i_gid != current->egid)) &&
 433             !suser()) {
 434                 retval = -EPERM;
 435                 goto exec_error2;
 436         }
 437         /* make sure we don't let suid, sgid files be ptraced. */
 438         if (current->flags & PF_PTRACED) {
 439                 e_uid = current->euid;
 440                 e_gid = current->egid;
 441         } else {
 442                 e_uid = (i & S_ISUID) ? inode->i_uid : current->euid;
 443                 e_gid = (i & S_ISGID) ? inode->i_gid : current->egid;
 444         }
 445         if (current->euid == inode->i_uid)
 446                 i >>= 6;
 447         else if (in_group_p(inode->i_gid))
 448                 i >>= 3;
 449         if (!(i & 1) &&
 450             !((inode->i_mode & 0111) && suser())) {
 451                 retval = -EACCES;
 452                 goto exec_error2;
 453         }
 454         if (!(bh = bread(inode->i_dev,bmap(inode,0),inode->i_sb->s_blocksize))) {
 455                 retval = -EACCES;
 456                 goto exec_error2;
 457         }
 458         if (!IS_RDONLY(inode)) {
 459                 inode->i_atime = CURRENT_TIME;
 460                 inode->i_dirt = 1;
 461         }
 462         ex = *((struct exec *) bh->b_data);     /* read exec-header */
 463         if ((bh->b_data[0] == '#') && (bh->b_data[1] == '!') && (!sh_bang)) {
 464                 /*
 465                  * This section does the #! interpretation.
 466                  * Sorta complicated, but hopefully it will work.  -TYT
 467                  */
 468 
 469                 char buf[128], *cp, *interp, *i_name, *i_arg;
 470                 unsigned long old_fs;
 471 
 472                 strncpy(buf, bh->b_data+2, 127);
 473                 brelse(bh);
 474                 iput(inode);
 475                 buf[127] = '\0';
 476                 if (cp = strchr(buf, '\n')) {
 477                         *cp = '\0';
 478                         for (cp = buf; (*cp == ' ') || (*cp == '\t'); cp++);
 479                 }
 480                 if (!cp || *cp == '\0') {
 481                         retval = -ENOEXEC; /* No interpreter name found */
 482                         goto exec_error1;
 483                 }
 484                 interp = i_name = cp;
 485                 i_arg = 0;
 486                 for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++) {
 487                         if (*cp == '/')
 488                                 i_name = cp+1;
 489                 }
 490                 if (*cp) {
 491                         *cp++ = '\0';
 492                         i_arg = cp;
 493                 }
 494                 /*
 495                  * OK, we've parsed out the interpreter name and
 496                  * (optional) argument.
 497                  */
 498                 if (sh_bang++ == 0) {
 499                         p = copy_strings(envc, envp, page, p, 0);
 500                         p = copy_strings(--argc, argv+1, page, p, 0);
 501                 }
 502                 /*
 503                  * Splice in (1) the interpreter's name for argv[0]
 504                  *           (2) (optional) argument to interpreter
 505                  *           (3) filename of shell script
 506                  *
 507                  * This is done in reverse order, because of how the
 508                  * user environment and arguments are stored.
 509                  */
 510                 p = copy_strings(1, &filename, page, p, 1);
 511                 argc++;
 512                 if (i_arg) {
 513                         p = copy_strings(1, &i_arg, page, p, 2);
 514                         argc++;
 515                 }
 516                 p = copy_strings(1, &i_name, page, p, 2);
 517                 argc++;
 518                 if (!p) {
 519                         retval = -ENOMEM;
 520                         goto exec_error1;
 521                 }
 522                 /*
 523                  * OK, now restart the process with the interpreter's inode.
 524                  */
 525                 old_fs = get_fs();
 526                 set_fs(get_ds());
 527                 retval = namei(interp,&inode);
 528                 set_fs(old_fs);
 529                 if (retval)
 530                         goto exec_error1;
 531                 goto restart_interp;
 532         }
 533         brelse(bh);
 534         if ((N_MAGIC(ex) != ZMAGIC && N_MAGIC(ex) != OMAGIC) ||
 535                 ex.a_trsize || ex.a_drsize ||
 536                 ex.a_text+ex.a_data+ex.a_bss>0x3000000 ||
 537                 inode->i_size < ex.a_text+ex.a_data+ex.a_syms+N_TXTOFF(ex)) {
 538                 retval = -ENOEXEC;
 539                 goto exec_error2;
 540         }
 541         if (N_TXTOFF(ex) != BLOCK_SIZE && N_MAGIC(ex) != OMAGIC) {
 542                 printk("%s: N_TXTOFF != BLOCK_SIZE. See a.out.h.", filename);
 543                 retval = -ENOEXEC;
 544                 goto exec_error2;
 545         }
 546         if (!sh_bang) {
 547                 p = copy_strings(envc,envp,page,p,0);
 548                 p = copy_strings(argc,argv,page,p,0);
 549                 if (!p) {
 550                         retval = -ENOMEM;
 551                         goto exec_error2;
 552                 }
 553         }
 554 /* OK, This is the point of no return */
 555         current->dumpable = 1;
 556         for (i=0; (ch = get_fs_byte(filename++)) != '\0';)
 557                 if (ch == '/')
 558                         i = 0;
 559                 else
 560                         if (i < 8)
 561                                 current->comm[i++] = ch;
 562         if (i < 8)
 563                 current->comm[i] = '\0';
 564         if (current->executable)
 565                 iput(current->executable);
 566         i = current->numlibraries;
 567         while (i-- > 0) {
 568                 iput(current->libraries[i].library);
 569                 current->libraries[i].library = NULL;
 570         }
 571         if (e_uid != current->euid || e_gid != current->egid ||
 572             !permission(inode,MAY_READ))
 573                 current->dumpable = 0;
 574         current->numlibraries = 0;
 575         current->executable = inode;
 576         current->signal = 0;
 577         for (i=0 ; i<32 ; i++) {
 578                 current->sigaction[i].sa_mask = 0;
 579                 current->sigaction[i].sa_flags = 0;
 580                 if (current->sigaction[i].sa_handler != SIG_IGN)
 581                         current->sigaction[i].sa_handler = NULL;
 582         }
 583         for (i=0 ; i<NR_OPEN ; i++)
 584                 if ((current->close_on_exec>>i)&1)
 585                         sys_close(i);
 586         current->close_on_exec = 0;
 587         clear_page_tables(current);
 588         if (last_task_used_math == current)
 589                 last_task_used_math = NULL;
 590         current->used_math = 0;
 591         p += change_ldt(ex.a_text,page);
 592         p -= MAX_ARG_PAGES*PAGE_SIZE;
 593         p = (unsigned long) create_tables((char *)p,argc,envc);
 594         current->brk = ex.a_bss +
 595                 (current->end_data = ex.a_data +
 596                 (current->end_code = ex.a_text));
 597         current->start_stack = p;
 598         current->rss = (TASK_SIZE - p + PAGE_SIZE-1) / PAGE_SIZE;
 599         current->suid = current->euid = e_uid;
 600         current->sgid = current->egid = e_gid;
 601         if (N_MAGIC(ex) == OMAGIC)
 602                 read_omagic(inode, ex.a_text+ex.a_data);
 603         eip[0] = ex.a_entry;            /* eip, magic happens :-) */
 604         eip[3] = p;                     /* stack pointer */
 605         if (current->flags & PF_PTRACED)
 606                 send_sig(SIGTRAP, current, 0);
 607         return 0;
 608 exec_error2:
 609         iput(inode);
 610 exec_error1:
 611         for (i=0 ; i<MAX_ARG_PAGES ; i++)
 612                 free_page(page[i]);
 613         return(retval);
 614 }

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