Apply --rmenv immediately to help to avoid the env var length check

Remove environment variables with --rmenv immediately. This fixes
removing long environment variables (LS_COLORS generated by vivid),
previously the length filter would trip before the command was
processed.

This changes user visible behavior slightly, for example --rmenv=LANG
now applies also to Firejail, while earlier it would only apply to
sandboxed program.

Partially fixes #3673, but not handling `rmenv` in profiles.

Also suggest --rmenv when there are problems with enviroment
variables.

Signed-off-by: Topi Miettinen <[email protected]>

src/firejail/main.c

@@ -1004,17 +1004,21 @@ int main(int argc, char **argv, char **envp) {
  fprintf(stderr, "Error: too long arguments\n");
  exit(1);
  }
+ // Also remove requested environment variables
+ // entirely to avoid tripping the length check below
+ if (strncmp(argv[i], "--rmenv=", 8) == 0)
+ unsetenv(argv[i] + 8);
  }
 
  // sanity check for environment variables
  for (i = 0, ptr = envp; ptr && *ptr && i < MAX_ENVS; i++, ptr++) {
  if (strlen(*ptr) >= MAX_ENV_LEN) {
- fprintf(stderr, "Error: too long environment variables\n");
+ fprintf(stderr, "Error: too long environment variables, please use --rmenv\n");
  exit(1);
  }
  }
  if (i >= MAX_ENVS) {
- fprintf(stderr, "Error: too many environment variables\n");
+ fprintf(stderr, "Error: too many environment variables, please use --rmenv\n");
  exit(1);
  }
 

src/firejail/profile.c

@@ -912,6 +912,7 @@ int profile_check_line(char *ptr, int lineno, const char *fname) {
  return 0;
  }
  if (strncmp(ptr, "rmenv ", 6) == 0) {
+ unsetenv(ptr + 6); // Remove also immediately from Firejail itself
  env_store(ptr + 6, RMENV);
  return 0;
  }