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fix TZ parsing logic for identifying POSIX-form strings

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previously, the contents of the TZ variable were considered a
candidate for a file/path name only if they began with a colon or
contained a slash before any comma. the latter was very sloppy logic
to avoid treating any valid POSIX TZ string as a file name, but it
also triggered on values that are not valid POSIX TZ strings,
including 3-letter timezone names without any offset.

instead, only treat the TZ variable as POSIX form if it begins with a
nonzero standard time name followed by +, -, or a digit.

also, special case GMT and UTC to always be treated as POSIX form
(with implicit zero offset) so that a stray file by the same name
cannot break software that depends on setting TZ=GMT or TZ=UTC.
This commit is contained in:
Rich Felker 2021-06-23 17:22:47 -04:00
parent 1f0c7cb1cc
commit 937822abb6
1 changed files with 13 additions and 1 deletions
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14
src/time/__tz.c
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@ -4,6 +4,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <ctype.h>
#include "libc.h"
#include "lock.h"
#include "fork_impl.h"
@ -154,10 +155,21 @@ static void do_tzset()
}
if (old_tz) memcpy(old_tz, s, i+1);
int posix_form = 0;
if (*s != ':') {
p = s;
char dummy_name[TZNAME_MAX+1];
getname(dummy_name, &p);
if (p!=s && (*p == '+' || *p == '-' || isdigit(*p)
|| !strcmp(dummy_name, "UTC")
|| !strcmp(dummy_name, "GMT")))
posix_form = 1;
}
/* Non-suid can use an absolute tzfile pathname or a relative
* pathame beginning with "."; in secure mode, only the
* standard path will be searched. */
if (*s == ':' || ((p=strchr(s, '/')) && !memchr(s, ',', p-s))) {
if (!posix_form) {
if (*s == ':') s++;
if (*s == '/' || *s == '.') {
if (!libc.secure || !strcmp(s, "/etc/localtime"))