1818#include "postgres_fe.h"
1919#endif
2020
21+ #include "common/sha2.h"
22+
2123#include <fcntl.h>
2224#include <unistd.h>
2325
2931#endif
3032
3133static bool random_from_file (char * filename ,void * buf ,size_t len );
34+ #ifndef WIN32
35+ static bool random_from_std (void * dst ,size_t len );
36+ #endif
3237
3338#ifdef WIN32
3439/*
@@ -72,6 +77,67 @@ random_from_file(char *filename, void *buf, size_t len)
7277return true;
7378}
7479
80+ #ifndef WIN32
81+ /*
82+ * This is not available on Windows, and the cryptography standards available
83+ * there are enough anyway to generate randomness.
84+ */
85+ #include <sys/time.h>
86+ #include <time.h>
87+
88+ /*
89+ * Generate some random data using environment data as entropy
90+ * through SHA-256. All the other methods failed, this can be used
91+ * as a last resort method even if it is predictible, and rather
92+ * slow compared to the rest.
93+ */
94+ static bool
95+ random_from_std (void * dst ,size_t len )
96+ {
97+ pid_t pid ;
98+ size_t remaining = len ;
99+
100+ /* process ID */
101+ pid = getpid ();
102+
103+ /*
104+ * Compute a random value by generating successive chunks worth
105+ * of PG_SHA256_DIGEST_LENGTH bytes.
106+ */
107+ while (remaining != 0 )
108+ {
109+ int x ;
110+ struct timeval tv ;
111+ pg_sha256_ctx ctx ;
112+ uint8 sha_buf [PG_SHA256_DIGEST_LENGTH ];
113+
114+ pg_sha256_init (& ctx );
115+ pg_sha256_update (& ctx , (uint8 * )& pid ,sizeof (pid ));
116+
117+ /* time */
118+ gettimeofday (& tv ,NULL );
119+ pg_sha256_update (& ctx , (uint8 * )& tv ,sizeof (tv ));
120+
121+ /* pointless, but should not hurt */
122+ x = random ();
123+ pg_sha256_update (& ctx , (uint8 * )& x ,sizeof (x ));
124+ pg_sha256_final (& ctx ,sha_buf );
125+
126+ /* copy the chunk generated in the result */
127+ memcpy (dst ,sha_buf ,Min (remaining ,PG_SHA256_DIGEST_LENGTH ));
128+
129+ /* and prepare to loop further */
130+ if (remaining >=PG_SHA256_DIGEST_LENGTH )
131+ remaining -= PG_SHA256_DIGEST_LENGTH ;
132+ else
133+ remaining = 0 ;
134+ dst = (uint8 * )dst + PG_SHA256_DIGEST_LENGTH ;
135+ }
136+
137+ return true;
138+ }
139+ #endif
140+
75141/*
76142 * pg_strong_random
77143 *
@@ -86,6 +152,8 @@ random_from_file(char *filename, void *buf, size_t len)
86152 * 2. Windows' CryptGenRandom() function
87153 * 3. /dev/urandom
88154 * 4. /dev/random
155+ * 5. Use the internal, predictible method computing a value through SHA-256
156+ * with system-related entropy.
89157 *
90158 * Returns true on success, and false if none of the sources
91159 * were available. NB: It is important to check the return value!
@@ -143,6 +211,14 @@ pg_strong_random(void *buf, size_t len)
143211if (random_from_file ("/dev/random" ,buf ,len ))
144212return true;
145213
214+ #ifndef WIN32
215+ /*
216+ * As final method, generate some randomness using the in-house method.
217+ */
218+ if (random_from_std (buf ,len ))
219+ return true;
220+ #endif
221+
146222/* None of the sources were available. */
147223return false;
148224}