1 /*-
2  * Copyright (c) 1990, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * This code is derived from software contributed to Berkeley by
6  * Chris Torek.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. Neither the name of the University nor the names of its contributors
17  *    may be used to endorse or promote products derived from this software
18  *    without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  */
32 
33 #include <errno.h>
34 #include <signal.h>
35 #include <stdio.h>
36 #include <stdlib.h>
37 #include <sys/stat.h>
38 #include <sys/types.h>
39 #include <unistd.h>
40 
41 #include "private/ErrnoRestorer.h"
42 
43 class ScopedSignalBlocker {
44  public:
ScopedSignalBlocker()45   ScopedSignalBlocker() {
46     sigset_t set;
47     sigfillset(&set);
48     sigprocmask(SIG_BLOCK, &set, &old_set_);
49   }
50 
~ScopedSignalBlocker()51   ~ScopedSignalBlocker() {
52     sigprocmask(SIG_SETMASK, &old_set_, NULL);
53   }
54 
55  private:
56   sigset_t old_set_;
57 };
58 
__tmpfile_dir(const char * tmp_dir)59 static FILE* __tmpfile_dir(const char* tmp_dir) {
60   char* path = NULL;
61   if (asprintf(&path, "%s/tmp.XXXXXXXXXX", tmp_dir) == -1) {
62     return NULL;
63   }
64 
65   int fd;
66   {
67     ScopedSignalBlocker ssb;
68     fd = mkstemp(path);
69     if (fd == -1) {
70       free(path);
71       return NULL;
72     }
73 
74     // Unlink the file now so that it's removed when closed.
75     unlink(path);
76     free(path);
77 
78     // Can we still use the file now it's unlinked?
79     // File systems without hard link support won't have the usual Unix semantics.
80     struct stat sb;
81     int rc = fstat(fd, &sb);
82     if (rc == -1) {
83       ErrnoRestorer errno_restorer;
84       close(fd);
85       return NULL;
86     }
87   }
88 
89   // Turn the file descriptor into a FILE*.
90   FILE* fp = fdopen(fd, "w+");
91   if (fp != NULL) {
92     return fp;
93   }
94 
95   // Failure. Clean up. We already unlinked, so we just need to close.
96   ErrnoRestorer errno_restorer;
97   close(fd);
98   return NULL;
99 }
100 
tmpfile()101 FILE* tmpfile() {
102   // TODO: get this app's temporary directory from the framework ("/data/data/app/cache").
103 
104   // $EXTERNAL_STORAGE turns out not to be very useful because it doesn't support hard links.
105   // This means we can't do the usual trick of calling unlink before handing the file back.
106 
107   FILE* fp = __tmpfile_dir("/data/local/tmp");
108   if (fp == NULL) {
109     // P_tmpdir is "/tmp/", but POSIX explicitly says that tmpdir(3) should try P_tmpdir before
110     // giving up. This is potentially useful for bionic on the host anyway.
111     fp = __tmpfile_dir(P_tmpdir);
112   }
113   return fp;
114 }
115 __strong_alias(tmpfile64, tmpfile);
116