1/* modechange.c -- file mode manipulation
2
3   Copyright (C) 1989, 1990, 1997, 1998, 1999, 2001, 2003, 2004, 2005,
4   2006 Free Software Foundation, Inc.
5
6   This program is free software: you can redistribute it and/or modify
7   it under the terms of the GNU General Public License as published by
8   the Free Software Foundation; either version 3 of the License, or
9   (at your option) any later version.
10
11   This program is distributed in the hope that it will be useful,
12   but WITHOUT ANY WARRANTY; without even the implied warranty of
13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14   GNU General Public License for more details.
15
16   You should have received a copy of the GNU General Public License
17   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
18
19/* Written by David MacKenzie <djm@ai.mit.edu> */
20
21/* The ASCII mode string is compiled into an array of `struct
22   modechange', which can then be applied to each file to be changed.
23   We do this instead of re-parsing the ASCII string for each file
24   because the compiled form requires less computation to use; when
25   changing the mode of many files, this probably results in a
26   performance gain.  */
27
28#include <config.h>
29
30#include "modechange.h"
31#include <sys/stat.h>
32#include "stat-macros.h"
33#include "xalloc.h"
34#include <stdlib.h>
35
36/* The traditional octal values corresponding to each mode bit.  */
37#define SUID 04000
38#define SGID 02000
39#define SVTX 01000
40#define RUSR 00400
41#define WUSR 00200
42#define XUSR 00100
43#define RGRP 00040
44#define WGRP 00020
45#define XGRP 00010
46#define ROTH 00004
47#define WOTH 00002
48#define XOTH 00001
49#define ALLM 07777 /* all octal mode bits */
50
51/* Convert OCTAL, which uses one of the traditional octal values, to
52   an internal mode_t value.  */
53static mode_t
54octal_to_mode (unsigned int octal)
55{
56  /* Help the compiler optimize the usual case where mode_t uses
57     the traditional octal representation.  */
58  return ((S_ISUID == SUID && S_ISGID == SGID && S_ISVTX == SVTX
59	   && S_IRUSR == RUSR && S_IWUSR == WUSR && S_IXUSR == XUSR
60	   && S_IRGRP == RGRP && S_IWGRP == WGRP && S_IXGRP == XGRP
61	   && S_IROTH == ROTH && S_IWOTH == WOTH && S_IXOTH == XOTH)
62	  ? octal
63	  : (mode_t) ((octal & SUID ? S_ISUID : 0)
64		      | (octal & SGID ? S_ISGID : 0)
65		      | (octal & SVTX ? S_ISVTX : 0)
66		      | (octal & RUSR ? S_IRUSR : 0)
67		      | (octal & WUSR ? S_IWUSR : 0)
68		      | (octal & XUSR ? S_IXUSR : 0)
69		      | (octal & RGRP ? S_IRGRP : 0)
70		      | (octal & WGRP ? S_IWGRP : 0)
71		      | (octal & XGRP ? S_IXGRP : 0)
72		      | (octal & ROTH ? S_IROTH : 0)
73		      | (octal & WOTH ? S_IWOTH : 0)
74		      | (octal & XOTH ? S_IXOTH : 0)));
75}
76
77/* Special operations flags.  */
78enum
79  {
80    /* For the sentinel at the end of the mode changes array.  */
81    MODE_DONE,
82
83    /* The typical case.  */
84    MODE_ORDINARY_CHANGE,
85
86    /* In addition to the typical case, affect the execute bits if at
87       least one execute bit is set already, or if the file is a
88       directory.  */
89    MODE_X_IF_ANY_X,
90
91    /* Instead of the typical case, copy some existing permissions for
92       u, g, or o onto the other two.  Which of u, g, or o is copied
93       is determined by which bits are set in the `value' field.  */
94    MODE_COPY_EXISTING
95  };
96
97/* Description of a mode change.  */
98struct mode_change
99{
100  char op;			/* One of "=+-".  */
101  char flag;			/* Special operations flag.  */
102  mode_t affected;		/* Set for u, g, o, or a.  */
103  mode_t value;			/* Bits to add/remove.  */
104  mode_t mentioned;		/* Bits explicitly mentioned.  */
105};
106
107/* Return a mode_change array with the specified `=ddd'-style
108   mode change operation, where NEW_MODE is `ddd' and MENTIONED
109   contains the bits explicitly mentioned in the mode are MENTIONED.  */
110
111static struct mode_change *
112make_node_op_equals (mode_t new_mode, mode_t mentioned)
113{
114  struct mode_change *p = xmalloc (2 * sizeof *p);
115  p->op = '=';
116  p->flag = MODE_ORDINARY_CHANGE;
117  p->affected = CHMOD_MODE_BITS;
118  p->value = new_mode;
119  p->mentioned = mentioned;
120  p[1].flag = MODE_DONE;
121  return p;
122}
123
124/* Return a pointer to an array of file mode change operations created from
125   MODE_STRING, an ASCII string that contains either an octal number
126   specifying an absolute mode, or symbolic mode change operations with
127   the form:
128   [ugoa...][[+-=][rwxXstugo...]...][,...]
129
130   Return NULL if `mode_string' does not contain a valid
131   representation of file mode change operations.  */
132
133struct mode_change *
134mode_compile (char const *mode_string)
135{
136  /* The array of mode-change directives to be returned.  */
137  struct mode_change *mc;
138  size_t used = 0;
139
140  if ('0' <= *mode_string && *mode_string < '8')
141    {
142      unsigned int octal_mode = 0;
143      mode_t mode;
144      mode_t mentioned;
145
146      do
147	{
148	  octal_mode = 8 * octal_mode + *mode_string++ - '0';
149	  if (ALLM < octal_mode)
150	    return NULL;
151	}
152      while ('0' <= *mode_string && *mode_string < '8');
153
154      if (*mode_string)
155	return NULL;
156
157      mode = octal_to_mode (octal_mode);
158      mentioned = (mode & (S_ISUID | S_ISGID)) | S_ISVTX | S_IRWXUGO;
159      return make_node_op_equals (mode, mentioned);
160    }
161
162  /* Allocate enough space to hold the result.  */
163  {
164    size_t needed = 1;
165    char const *p;
166    for (p = mode_string; *p; p++)
167      needed += (*p == '=' || *p == '+' || *p == '-');
168    mc = xnmalloc (needed, sizeof *mc);
169  }
170
171  /* One loop iteration for each `[ugoa]*([-+=]([rwxXst]*|[ugo]))+'.  */
172  for (;; mode_string++)
173    {
174      /* Which bits in the mode are operated on.  */
175      mode_t affected = 0;
176
177      /* Turn on all the bits in `affected' for each group given.  */
178      for (;; mode_string++)
179	switch (*mode_string)
180	  {
181	  default:
182	    goto invalid;
183	  case 'u':
184	    affected |= S_ISUID | S_IRWXU;
185	    break;
186	  case 'g':
187	    affected |= S_ISGID | S_IRWXG;
188	    break;
189	  case 'o':
190	    affected |= S_ISVTX | S_IRWXO;
191	    break;
192	  case 'a':
193	    affected |= CHMOD_MODE_BITS;
194	    break;
195	  case '=': case '+': case '-':
196	    goto no_more_affected;
197	  }
198    no_more_affected:;
199
200      do
201	{
202	  char op = *mode_string++;
203	  mode_t value;
204	  char flag = MODE_COPY_EXISTING;
205	  struct mode_change *change;
206
207	  switch (*mode_string++)
208	    {
209	    case 'u':
210	      /* Set the affected bits to the value of the `u' bits
211		 on the same file.  */
212	      value = S_IRWXU;
213	      break;
214	    case 'g':
215	      /* Set the affected bits to the value of the `g' bits
216		 on the same file.  */
217	      value = S_IRWXG;
218	      break;
219	    case 'o':
220	      /* Set the affected bits to the value of the `o' bits
221		 on the same file.  */
222	      value = S_IRWXO;
223	      break;
224
225	    default:
226	      value = 0;
227	      flag = MODE_ORDINARY_CHANGE;
228
229	      for (mode_string--;; mode_string++)
230		switch (*mode_string)
231		  {
232		  case 'r':
233		    value |= S_IRUSR | S_IRGRP | S_IROTH;
234		    break;
235		  case 'w':
236		    value |= S_IWUSR | S_IWGRP | S_IWOTH;
237		    break;
238		  case 'x':
239		    value |= S_IXUSR | S_IXGRP | S_IXOTH;
240		    break;
241		  case 'X':
242		    flag = MODE_X_IF_ANY_X;
243		    break;
244		  case 's':
245		    /* Set the setuid/gid bits if `u' or `g' is selected.  */
246		    value |= S_ISUID | S_ISGID;
247		    break;
248		  case 't':
249		    /* Set the "save text image" bit if `o' is selected.  */
250		    value |= S_ISVTX;
251		    break;
252		  default:
253		    goto no_more_values;
254		  }
255	    no_more_values:;
256	    }
257
258	  change = &mc[used++];
259	  change->op = op;
260	  change->flag = flag;
261	  change->affected = affected;
262	  change->value = value;
263	  change->mentioned = (affected ? affected & value : value);
264	}
265      while (*mode_string == '=' || *mode_string == '+'
266	     || *mode_string == '-');
267
268      if (*mode_string != ',')
269	break;
270    }
271
272  if (*mode_string == 0)
273    {
274      mc[used].flag = MODE_DONE;
275      return mc;
276    }
277
278invalid:
279  free (mc);
280  return NULL;
281}
282
283/* Return a file mode change operation that sets permissions to match those
284   of REF_FILE.  Return NULL (setting errno) if REF_FILE can't be accessed.  */
285
286struct mode_change *
287mode_create_from_ref (const char *ref_file)
288{
289  struct stat ref_stats;
290
291  if (stat (ref_file, &ref_stats) != 0)
292    return NULL;
293  return make_node_op_equals (ref_stats.st_mode, CHMOD_MODE_BITS);
294}
295
296/* Return the file mode bits of OLDMODE (which is the mode of a
297   directory if DIR), assuming the umask is UMASK_VALUE, adjusted as
298   indicated by the list of change operations CHANGES.  If DIR, the
299   type 'X' change affects the returned value even if no execute bits
300   were set in OLDMODE, and set user and group ID bits are preserved
301   unless CHANGES mentioned them.  If PMODE_BITS is not null, store into
302   *PMODE_BITS a mask denoting file mode bits that are affected by
303   CHANGES.
304
305   The returned value and *PMODE_BITS contain only file mode bits.
306   For example, they have the S_IFMT bits cleared on a standard
307   Unix-like host.  */
308
309mode_t
310mode_adjust (mode_t oldmode, bool dir, mode_t umask_value,
311	     struct mode_change const *changes, mode_t *pmode_bits)
312{
313  /* The adjusted mode.  */
314  mode_t newmode = oldmode & CHMOD_MODE_BITS;
315
316  /* File mode bits that CHANGES cares about.  */
317  mode_t mode_bits = 0;
318
319  for (; changes->flag != MODE_DONE; changes++)
320    {
321      mode_t affected = changes->affected;
322      mode_t omit_change =
323	(dir ? S_ISUID | S_ISGID : 0) & ~ changes->mentioned;
324      mode_t value = changes->value;
325
326      switch (changes->flag)
327	{
328	case MODE_ORDINARY_CHANGE:
329	  break;
330
331	case MODE_COPY_EXISTING:
332	  /* Isolate in `value' the bits in `newmode' to copy.  */
333	  value &= newmode;
334
335	  /* Copy the isolated bits to the other two parts.  */
336	  value |= ((value & (S_IRUSR | S_IRGRP | S_IROTH)
337		     ? S_IRUSR | S_IRGRP | S_IROTH : 0)
338		    | (value & (S_IWUSR | S_IWGRP | S_IWOTH)
339		       ? S_IWUSR | S_IWGRP | S_IWOTH : 0)
340		    | (value & (S_IXUSR | S_IXGRP | S_IXOTH)
341		       ? S_IXUSR | S_IXGRP | S_IXOTH : 0));
342	  break;
343
344	case MODE_X_IF_ANY_X:
345	  /* Affect the execute bits if execute bits are already set
346	     or if the file is a directory.  */
347	  if ((newmode & (S_IXUSR | S_IXGRP | S_IXOTH)) | dir)
348	    value |= S_IXUSR | S_IXGRP | S_IXOTH;
349	  break;
350	}
351
352      /* If WHO was specified, limit the change to the affected bits.
353	 Otherwise, apply the umask.  Either way, omit changes as
354	 requested.  */
355      value &= (affected ? affected : ~umask_value) & ~ omit_change;
356
357      switch (changes->op)
358	{
359	case '=':
360	  /* If WHO was specified, preserve the previous values of
361	     bits that are not affected by this change operation.
362	     Otherwise, clear all the bits.  */
363	  {
364	    mode_t preserved = (affected ? ~affected : 0) | omit_change;
365	    mode_bits |= CHMOD_MODE_BITS & ~preserved;
366	    newmode = (newmode & preserved) | value;
367	    break;
368	  }
369
370	case '+':
371	  mode_bits |= value;
372	  newmode |= value;
373	  break;
374
375	case '-':
376	  mode_bits |= value;
377	  newmode &= ~value;
378	  break;
379	}
380    }
381
382  if (pmode_bits)
383    *pmode_bits = mode_bits;
384  return newmode;
385}
386