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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 buf[PATH_MAX];
61   int path_length = snprintf(buf, sizeof(buf), "%s/tmp.XXXXXXXXXX", tmp_dir);
62   if (path_length >= static_cast<int>(sizeof(buf))) {
63     return NULL;
64   }
65 
66   int fd;
67   {
68     ScopedSignalBlocker ssb;
69     fd = mkstemp(buf);
70     if (fd == -1) {
71       return NULL;
72     }
73 
74     // Unlink the file now so that it's removed when closed.
75     unlink(buf);
76 
77     // Can we still use the file now it's unlinked?
78     // File systems without hard link support won't have the usual Unix semantics.
79     struct stat sb;
80     int rc = fstat(fd, &sb);
81     if (rc == -1) {
82       ErrnoRestorer errno_restorer;
83       close(fd);
84       return NULL;
85     }
86   }
87 
88   // Turn the file descriptor into a FILE*.
89   FILE* fp = fdopen(fd, "w+");
90   if (fp != NULL) {
91     return fp;
92   }
93 
94   // Failure. Clean up. We already unlinked, so we just need to close.
95   ErrnoRestorer errno_restorer;
96   close(fd);
97   return NULL;
98 }
99 
tmpfile()100 FILE* tmpfile() {
101   // TODO: get this app's temporary directory from the framework ("/data/data/app/cache").
102 
103   // $EXTERNAL_STORAGE turns out not to be very useful because it doesn't support hard links.
104   // This means we can't do the usual trick of calling unlink before handing the file back.
105 
106   FILE* fp = __tmpfile_dir("/data/local/tmp");
107   if (fp == NULL) {
108     // P_tmpdir is "/tmp/", but POSIX explicitly says that tmpdir(3) should try P_tmpdir before
109     // giving up. This is potentially useful for bionic on the host anyway.
110     fp = __tmpfile_dir(P_tmpdir);
111   }
112   return fp;
113 }
114