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Commit11a0a8b

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committed
Implement find_my_exec()'s path normalization using realpath(3).
Replace the symlink-chasing logic in find_my_exec with realpath(3),which has been required by POSIX since SUSv2. (Windows lacksrealpath(), but there we can use _fullpath() which is functionallyequivalent.) The main benefit of this is that -- on all modernplatforms at least -- realpath() avoids the chdir() shenaniganswe used to perform while interpreting symlinks. That had variouscorner-case failure modes so it's good to get rid of it.There is still ongoing discussion about whether we could skip thereplacement of symlinks in some cases, but that's really matterfor a separate patch. Meanwhile I want to push this before we gettoo close to feature freeze, so that we can find out if there areshowstopper portability issues.Discussion:https://postgr.es/m/797232.1662075573@sss.pgh.pa.us
1 parenteb2618a commit11a0a8b

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1 file changed

+91
-115
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1 file changed

+91
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‎src/common/exec.c

Lines changed: 91 additions & 115 deletions
Original file line numberDiff line numberDiff line change
@@ -14,6 +14,15 @@
1414
*-------------------------------------------------------------------------
1515
*/
1616

17+
/*
18+
* On macOS, "man realpath" avers:
19+
* Defining _DARWIN_C_SOURCE or _DARWIN_BETTER_REALPATH before including
20+
* stdlib.h will cause the provided implementation of realpath() to use
21+
* F_GETPATH from fcntl(2) to discover the path.
22+
* This should be harmless everywhere else.
23+
*/
24+
#define_DARWIN_BETTER_REALPATH
25+
1726
#ifndefFRONTEND
1827
#include"postgres.h"
1928
#else
@@ -58,11 +67,8 @@ extern int_CRT_glob = 0;/* 0 turns off globbing; 1 turns it on */
5867
(fprintf(stderr, __VA_ARGS__), fputc('\n', stderr))
5968
#endif
6069

61-
#ifdef_MSC_VER
62-
#definegetcwd(cwd,len) GetCurrentDirectory(len, cwd)
63-
#endif
64-
65-
staticintresolve_symlinks(char*path);
70+
staticintnormalize_exec_path(char*path);
71+
staticchar*pg_realpath(constchar*fname);
6672

6773
#ifdefWIN32
6874
staticBOOLGetTokenUser(HANDLEhToken,PTOKEN_USER*ppTokenUser);
@@ -87,7 +93,7 @@ validate_exec(const char *path)
8793
charpath_exe[MAXPGPATH+sizeof(".exe")-1];
8894

8995
/* Win32 requires a .exe suffix for stat() */
90-
if (strlen(path)>=strlen(".exe")&&
96+
if (strlen(path)<strlen(".exe")||
9197
pg_strcasecmp(path+strlen(path)-strlen(".exe"),".exe")!=0)
9298
{
9399
strlcpy(path_exe,path,sizeof(path_exe)-4);
@@ -135,46 +141,32 @@ validate_exec(const char *path)
135141

136142

137143
/*
138-
* find_my_exec -- find an absolute path toa valid executable
144+
* find_my_exec -- find an absolute path tothis program's executable
139145
*
140146
*argv0 is the name passed on the command line
141147
*retpath is the output area (must be of size MAXPGPATH)
142148
*Returns 0 if OK, -1 if error.
143149
*
144150
* The reason we have to work so hard to find an absolute path is that
145151
* on some platforms we can't do dynamic loading unless we know the
146-
* executable's location. Also, we needa full path not a relative
147-
* path because wewill later change working directory. Finally, we want
152+
* executable's location. Also, we needan absolute path not a relative
153+
* path because wemay later change working directory. Finally, we want
148154
* a true path not a symlink location, so that we can locate other files
149155
* that are part of our installation relative to the executable.
150156
*/
151157
int
152158
find_my_exec(constchar*argv0,char*retpath)
153159
{
154-
charcwd[MAXPGPATH],
155-
test_path[MAXPGPATH];
156160
char*path;
157161

158-
if (!getcwd(cwd,MAXPGPATH))
159-
{
160-
log_error(errcode_for_file_access(),
161-
_("could not identify current directory: %m"));
162-
return-1;
163-
}
164-
165162
/*
166163
* If argv0 contains a separator, then PATH wasn't used.
167164
*/
168-
if (first_dir_separator(argv0)!=NULL)
165+
strlcpy(retpath,argv0,MAXPGPATH);
166+
if (first_dir_separator(retpath)!=NULL)
169167
{
170-
if (is_absolute_path(argv0))
171-
strlcpy(retpath,argv0,MAXPGPATH);
172-
else
173-
join_path_components(retpath,cwd,argv0);
174-
canonicalize_path(retpath);
175-
176168
if (validate_exec(retpath)==0)
177-
returnresolve_symlinks(retpath);
169+
returnnormalize_exec_path(retpath);
178170

179171
log_error(errcode(ERRCODE_WRONG_OBJECT_TYPE),
180172
_("invalid binary \"%s\": %m"),retpath);
@@ -183,9 +175,8 @@ find_my_exec(const char *argv0, char *retpath)
183175

184176
#ifdefWIN32
185177
/* Win32 checks the current directory first for names without slashes */
186-
join_path_components(retpath,cwd,argv0);
187178
if (validate_exec(retpath)==0)
188-
returnresolve_symlinks(retpath);
179+
returnnormalize_exec_path(retpath);
189180
#endif
190181

191182
/*
@@ -208,21 +199,15 @@ find_my_exec(const char *argv0, char *retpath)
208199
if (!endp)
209200
endp=startp+strlen(startp);/* point to end */
210201

211-
strlcpy(test_path,startp,Min(endp-startp+1,MAXPGPATH));
202+
strlcpy(retpath,startp,Min(endp-startp+1,MAXPGPATH));
212203

213-
if (is_absolute_path(test_path))
214-
join_path_components(retpath,test_path,argv0);
215-
else
216-
{
217-
join_path_components(retpath,cwd,test_path);
218-
join_path_components(retpath,retpath,argv0);
219-
}
204+
join_path_components(retpath,retpath,argv0);
220205
canonicalize_path(retpath);
221206

222207
switch (validate_exec(retpath))
223208
{
224209
case0:/* found ok */
225-
returnresolve_symlinks(retpath);
210+
returnnormalize_exec_path(retpath);
226211
case-1:/* wasn't even a candidate, keep looking */
227212
break;
228213
case-2:/* found but disqualified */
@@ -241,105 +226,96 @@ find_my_exec(const char *argv0, char *retpath)
241226

242227

243228
/*
244-
*resolve_symlinks - resolve symlinksto the underlying file
229+
*normalize_exec_path - resolve symlinksand convert to absolute path
245230
*
246-
* Replace "path" by the absolute path to the referenced file.
231+
* Given a path that refers to an executable, chase through any symlinks
232+
* to find the real file location; then convert that to an absolute path.
247233
*
234+
* On success, replaces the contents of "path" with the absolute path.
235+
* ("path" is assumed to be of size MAXPGPATH.)
248236
* Returns 0 if OK, -1 if error.
249-
*
250-
* Note: we are not particularly tense about producing nice error messages
251-
* because we are not really expecting error here; we just determined that
252-
* the symlink does point to a valid executable.
253-
*
254-
* Here we test HAVE_READLINK, which excludes Windows. There's no point in
255-
* using our junction point-based replacement code for this, because that only
256-
* works for directories.
257237
*/
258238
staticint
259-
resolve_symlinks(char*path)
239+
normalize_exec_path(char*path)
260240
{
261-
#ifdefHAVE_READLINK
262-
structstatbuf;
263-
charorig_wd[MAXPGPATH],
264-
link_buf[MAXPGPATH];
265-
char*fname;
266-
267241
/*
268-
* To resolve a symlink properly, we have to chdir into its directory and
269-
* then chdir to where the symlink points; otherwise we may fail to
270-
* resolve relative links correctly (consider cases involving mount
271-
* points, for example). After following the final symlink, we use
272-
* getcwd() to figure out where the heck we're at.
273-
*
274-
* One might think we could skip all this if path doesn't point to a
275-
* symlink to start with, but that's wrong. We also want to get rid of
276-
* any directory symlinks that are present in the given path. We expect
277-
* getcwd() to give us an accurate, symlink-free path.
242+
* We used to do a lot of work ourselves here, but now we just let
243+
* realpath(3) do all the heavy lifting.
278244
*/
279-
if (!getcwd(orig_wd,MAXPGPATH))
245+
char*abspath=pg_realpath(path);
246+
247+
if (abspath==NULL)
280248
{
281249
log_error(errcode_for_file_access(),
282-
_("could not identify current directory: %m"));
250+
_("could not resolve path \"%s\" to absolute form: %m"),
251+
path);
283252
return-1;
284253
}
254+
strlcpy(path,abspath,MAXPGPATH);
255+
free(abspath);
285256

286-
for (;;)
287-
{
288-
char*lsep;
289-
intrllen;
290-
291-
lsep=last_dir_separator(path);
292-
if (lsep)
293-
{
294-
*lsep='\0';
295-
if (chdir(path)==-1)
296-
{
297-
log_error(errcode_for_file_access(),
298-
_("could not change directory to \"%s\": %m"),path);
299-
return-1;
300-
}
301-
fname=lsep+1;
302-
}
303-
else
304-
fname=path;
257+
#ifdefWIN32
258+
/* On Windows, be sure to convert '\' to '/' */
259+
canonicalize_path(path);
260+
#endif
305261

306-
if (lstat(fname,&buf)<0||
307-
!S_ISLNK(buf.st_mode))
308-
break;
262+
return0;
263+
}
309264

310-
errno=0;
311-
rllen=readlink(fname,link_buf,sizeof(link_buf));
312-
if (rllen<0||rllen >=sizeof(link_buf))
313-
{
314-
log_error(errcode_for_file_access(),
315-
_("could not read symbolic link \"%s\": %m"),fname);
316-
return-1;
317-
}
318-
link_buf[rllen]='\0';
319-
strcpy(path,link_buf);
320-
}
321265

322-
/* must copy final component out of 'path' temporarily */
323-
strlcpy(link_buf,fname,sizeof(link_buf));
266+
/*
267+
* pg_realpath() - realpath(3) with POSIX.1-2008 semantics
268+
*
269+
* This is equivalent to realpath(fname, NULL), in that it returns a
270+
* malloc'd buffer containing the absolute path equivalent to fname.
271+
* On error, returns NULL with errno set.
272+
*
273+
* On Windows, what you get is spelled per platform conventions,
274+
* so you probably want to apply canonicalize_path() to the result.
275+
*
276+
* For now, this is needed only here so mark it static. If you choose to
277+
* move it into its own file, move the _DARWIN_BETTER_REALPATH #define too!
278+
*/
279+
staticchar*
280+
pg_realpath(constchar*fname)
281+
{
282+
char*path;
324283

325-
if (!getcwd(path,MAXPGPATH))
284+
#ifndefWIN32
285+
path=realpath(fname,NULL);
286+
if (path==NULL&&errno==EINVAL)
326287
{
327-
log_error(errcode_for_file_access(),
328-
_("could not identify current directory: %m"));
329-
return-1;
330-
}
331-
join_path_components(path,path,link_buf);
332-
canonicalize_path(path);
288+
/*
289+
* Cope with old-POSIX systems that require a user-provided buffer.
290+
* Assume MAXPGPATH is enough room on all such systems.
291+
*/
292+
char*buf=malloc(MAXPGPATH);
333293

334-
if (chdir(orig_wd)==-1)
335-
{
336-
log_error(errcode_for_file_access(),
337-
_("could not change directory to \"%s\": %m"),orig_wd);
338-
return-1;
294+
if (buf==NULL)
295+
returnNULL;/* assume errno is set */
296+
path=realpath(fname,buf);
297+
if (path==NULL)/* don't leak memory */
298+
{
299+
intsave_errno=errno;
300+
301+
free(buf);
302+
errno=save_errno;
303+
}
339304
}
340-
#endif/*HAVE_READLINK */
305+
#else/*WIN32 */
341306

342-
return0;
307+
/*
308+
* Microsoft is resolutely non-POSIX, but _fullpath() does the same thing.
309+
* The documentation claims it reports errors by setting errno, which is a
310+
* bit surprising for Microsoft, but we'll believe that until it's proven
311+
* wrong. Clear errno first, though, so we can at least tell if a failure
312+
* occurs and doesn't set it.
313+
*/
314+
errno=0;
315+
path=_fullpath(NULL,fname,0);
316+
#endif
317+
318+
returnpath;
343319
}
344320

345321

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