severity critical thanks Hi Dirk, * Dirk Wetter <[EMAIL PROTECTED]> [2008-08-15 11:57]: > There's a problem with the randomness of mktemp. The > string includes a number which includes somewhat > the current process ID (based on the current PID). Worse: > Subsequent calls just seem to increase the number > by one:
The exact sequence is system dependent but looking at the
code the problem is obvious:
75 static int
76 _gettemp(path, doopen, domkdir)
77 char *path;
78 register int *doopen;
79 int domkdir;
80 {
81 register char *start, *trv;
82 struct stat sbuf;
83 int pid, rval;
84 char *alphabet =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
85
86 if (doopen && domkdir) {
87 errno = EINVAL;
88 return(0);
89 }
90
91 pid = getpid();
92 for (trv = path; *trv; ++trv)
93 ;
94 --trv;
95 while (trv >= path && *trv == 'X' && pid != 0) {
96 *trv-- = (pid % 10) + '0';
97 pid /= 10;
98 }
This is generating the numbers and the number here is only based on the pid.
This is no randomness at all. Depending on the pid number this will always
generate n non-random numbers at the end (for < 10000 4 numbers).
99 while (trv >= path && *trv == 'X') {
100 char c;
101
102 pid = (get_random() & 0xffff) % (26+26);
103 c = alphabet[pid];
104 *trv-- = c;
105 }
This is the alphabet part which looks fairly random to me (I am no crypto
expert though)
if _PATH_RANDOM is set which is the case for Debian.
I raised the severity to critical as a lot of shell scripts
in Debian rely on this data being random.
Kind regards
Nico
--
Nico Golde - http://www.ngolde.de - [EMAIL PROTECTED] - GPG: 0x73647CFF
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