From 71c3f623c6011c923788f0770ad40fe2756893a7 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Sat, 20 Apr 2019 02:51:51 -0500
Subject: New xsetenv() plumbing (repeatedly set same environment variables
 without leaking memory), and mod env command to test it.

---
 lib/env.c | 115 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 lib/env.c

(limited to 'lib/env.c')

diff --git a/lib/env.c b/lib/env.c
new file mode 100644
index 00000000..94ea0a4e
--- /dev/null
+++ b/lib/env.c
@@ -0,0 +1,115 @@
+// Can't trust libc not to leak enviornment variable memory, so...
+
+#include "toys.h"
+
+// In libc, populated by start code,used by getenv() and exec() and friends.
+extern char **environ;
+
+// Returns the number of bytes taken by the environment variables. For use
+// when calculating the maximum bytes of environment+argument data that can
+// be passed to exec for find(1) and xargs(1).
+long environ_bytes()
+{
+  long bytes = sizeof(char *);
+  char **ev;
+
+  for (ev = environ; *ev; ev++) bytes += sizeof(char *) + strlen(*ev) + 1;
+
+  return bytes;
+}
+
+// This will clear the inherited environment if called first thing.
+// Use this instead of envc so we keep track of what needs to be freed.
+void xclearenv(void)
+{
+  toys.envc = 0;
+  *environ = 0;
+}
+
+// Frees entries we set earlier. Use with libc getenv but not setenv/putenv.
+// if name has an equals and !val, act like putenv (name=val must be malloced!)
+// if !val unset name. (Name with = and val is an error)
+void xsetenv(char *name, char *val)
+{
+  unsigned i, len, envc;
+  char *new;
+
+  // If we haven't snapshot initial environment state yet, do so now.
+  if (!toys.envc) {
+    while (environ[toys.envc++]);
+    memcpy(new = xmalloc(((toys.envc|0xff)+1)*sizeof(char *)),
+      environ, toys.envc*sizeof(char *));
+    environ = (void *)new;
+  }
+
+  new = strchr(name, '=');
+  if (new) {
+    len = new-name;
+    if (val) error_exit("xsetenv %s to %s", name, val);
+    new = name;
+  } else {
+    len = strlen(name);
+    if (val) new = xmprintf("%s=%s", name, val);
+  }
+
+  envc = toys.envc-1;
+  for (i = 0; environ[i]; i++) {
+    // Drop old entry, freeing as appropriate. Assumes no duplicates.
+    if (!memcmp(name, environ[i], len) && environ[i][len]=='=') {
+      if (i>=envc) free(environ[i]);
+      else {
+        char **delete = environ+i;
+
+        // move old entries down, add at end of old data
+        toys.envc = envc--;
+        for (i=0; new ? i<envc : !!delete[i]; i++) delete[i] = delete[i+1];
+        i = envc;
+      }
+      break;
+    }
+  }
+
+  if (!new) return;
+
+  // resize and null terminate if expanding
+  if (!environ[i]) {
+    len = i+1;
+    if (!(len&255)) environ = xrealloc(environ, len*sizeof(char *));
+    environ[len] = 0;
+  }
+  environ[i] = new;
+}
+
+// reset environment for a user, optionally clearing most of it
+void reset_env(struct passwd *p, int clear)
+{
+  int i;
+
+  if (clear) {
+    char *s, *stuff[] = {"TERM", "DISPLAY", "COLORTERM", "XAUTHORITY"};
+
+    for (i=0; i<ARRAY_LEN(stuff); i++)
+      stuff[i] = (s = getenv(stuff[i])) ? xmprintf("%s=%s", stuff[i], s) : 0;
+    xclearenv();
+    for (i=0; i < ARRAY_LEN(stuff); i++) if (stuff[i]) xsetenv(stuff[i], 0);
+    if (chdir(p->pw_dir)) {
+      perror_msg("chdir %s", p->pw_dir);
+      xchdir("/");
+    }
+  } else {
+    char **ev1, **ev2;
+
+    // remove LD_*, IFS, ENV, and BASH_ENV from environment
+    for (ev1 = ev2 = environ;;) {
+      while (*ev2 && (strstart(ev2, "LD_") || strstart(ev2, "IFS=") ||
+        strstart(ev2, "ENV=") || strstart(ev2, "BASH_ENV="))) ev2++;
+      if (!(*ev1++ = *ev2++)) break;
+    }
+  }
+
+  setenv("PATH", _PATH_DEFPATH, 1);
+  setenv("HOME", p->pw_dir, 1);
+  setenv("SHELL", p->pw_shell, 1);
+  setenv("USER", p->pw_name, 1);
+  setenv("LOGNAME", p->pw_name, 1);
+}
-- 
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