Re: [PATCH] libgfortran: Fix up putenv uses in libcaf_shmem [PR124330]

[Jerry D]

On 3/4/26 7:44 AM, John David Anglin wrote:

Hi Jakub,

I believe this change is obvious.  The Linux manpage for putenv states:

        In particular, this string
        becomes part of the environment; changing it later will change the envi‐
        ronment.  (Thus, it is an error to call putenv() with an automatic vari‐
        able as the argument, then return from the calling function while string
        is still part of the environment.)

Some systems may have used a copy but this causes a memory leak.  On HP-UX, 
altering
the string changes the environment, so I believe it doesn't use a copy.  So, we 
want
a static string.

Thanks,
Dave

Yes, agree, OK for trunk.

Jerry

On 2026-03-04 10:12 a.m., Jakub Jelinek wrote:

Hi!

I don't have access to HP/UX, but at least on other OSes and what Linux as
well as POSIX documents is that when you call putenv with some argument,
what that argument points to becomes part of the environment and when
it is changed, the environment changes.  I believe ENOMEM from putenv is
about reallocating of the __environ (or similar) pointed array of pointers
(e.g. if the particular env var name isn't there already), it still
shouldn't allocate any memory for the NAME=VALUE string and just use
the user provided.  So, padding address of automatic array will be UB
as soon as the scope of that var is left.

One can either malloc the buffer, or use static vars, then nothing leaks
and in the unlikely case putenv would be called twice for the same env var,
it would second time only register the same buffer.

Ok for trunk?

2026-03-04  Jakub Jelinek  <ja...@redhat.com>

        PR libfortran/124330
        * caf/shmem/shared_memory.c (shared_memory_set_env): Make buffer
        used by putenv static.
        (shared_memory_init): Likewise.

--- libgfortran/caf/shmem/shared_memory.c.jj    2026-03-04 09:15:13.572332552 
+0100
+++ libgfortran/caf/shmem/shared_memory.c       2026-03-04 14:01:14.511957983 
+0100
@@ -71,7 +71,7 @@ shared_memory_set_env (pid_t pid)
    snprintf (val, 20, "%d", pid);
    SetEnvironmentVariable (ENV_PPID, val);
  #else
-  char buffer[28];
+  static char buffer[28];
    int res;

/* HP-UX / Legacy Fallback using putenv */

@@ -253,7 +253,7 @@ shared_memory_init (shared_memory_act *m
        snprintf (val, 20, "%p", mem->glbl.base);
        SetEnvironmentVariable (ENV_BASE, val);
  #else
-      char buffer[28];
+      static char buffer[28];
        int res;

/* HP-UX / Legacy Fallback using putenv */

        Jakub