[patch] timegm.3: copy the string returned by getenv()

[patch] timegm.3: copy the string returned by getenv()

[Jérémie Galarneau]

The example of a portable version of timegm() uses the string returned by
getenv() after calling setenv() on the same environment variale. The tz
string may be invalid as per getenv.3:

"The string pointed to by the return value of getenv() may be statically
allocated, and can be modified by a subsequent call to getenv(), putenv(3),
setenv(3), or unsetenv(3)."

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 man3/timegm.3 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/man3/timegm.3 b/man3/timegm.3
index 3ab194b..0e71be5 100644
--- a/man3/timegm.3
+++ b/man3/timegm.3
@@ -84,12 +84,15 @@ my_timegm(struct tm *tm)
     char *tz;
 
     tz = getenv("TZ");
+    if (tz)
+        tz = strdup(tz);
     setenv("TZ", "", 1);
     tzset();
     ret = mktime(tm);
-    if (tz)
+    if (tz) {
         setenv("TZ", tz, 1);
-    else
+        free(tz);
+    } else
         unsetenv("TZ");
     tzset();
     return ret;
-- 
1.8.3.1

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Re: [patch] timegm.3: copy the string returned by getenv()

[Michael Kerrisk]

On 06/26/13 17:08, Jérémie Galarneau wrote:
> The example of a portable version of timegm() uses the string returned by
> getenv() after calling setenv() on the same environment variale. The tz
> string may be invalid as per getenv.3:
> 
> "The string pointed to by the return value of getenv() may be statically
> allocated, and can be modified by a subsequent call to getenv(), putenv(3),
> setenv(3), or unsetenv(3)."
> 
> Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

Thanks, Jérémie. I've applied your patch.

Cheers,

Michael


> ---
>  man3/timegm.3 | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/man3/timegm.3 b/man3/timegm.3
> index 3ab194b..0e71be5 100644
> --- a/man3/timegm.3
> +++ b/man3/timegm.3
> @@ -84,12 +84,15 @@ my_timegm(struct tm *tm)
>      char *tz;
>  
>      tz = getenv("TZ");
> +    if (tz)
> +        tz = strdup(tz);
>      setenv("TZ", "", 1);
>      tzset();
>      ret = mktime(tm);
> -    if (tz)
> +    if (tz) {
>          setenv("TZ", tz, 1);
> -    else
> +        free(tz);
> +    } else
>          unsetenv("TZ");
>      tzset();
>      return ret;


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