ui-snapshot: do not access $HOME

It's a bit tedious to have to do this here too. If we encounter other
issues with $HOME down the line, I'll look into adding some nice utility
functions to handle this, or perhaps giving up on the hope that we could
keep $HOME defined for scripts.

This commit additionally adds a test case, should the issue surface
again.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

2 files changed, 10 insertions, 0 deletions

@@ -37,5 +37,6 @@ test_no_home_access_success foo/tree/file-1
 test_no_home_access_success foo/commit
 test_no_home_access_success foo/diff
 test_no_home_access_success foo/patch
+test_no_home_access_success foo/snapshot/master.tar.gz
 
 test_done
@@ -16,6 +16,7 @@ static int write_archive_type(const char *format, const char *hex, const char *p
 {
         struct argv_array argv = ARGV_ARRAY_INIT;
         const char **nargv;
+        char *user_home, *xdg_home;
         int result;
         argv_array_push(&argv, "snapshot");
         argv_array_push(&argv, format);
@@ -38,7 +39,15 @@ static int write_archive_type(const char *format, const char *hex, const char *p
         /* argv_array guarantees a trailing NULL entry. */
         memcpy(nargv, argv.argv, sizeof(char *) * (argv.argc + 1));
 
+        user_home = getenv("HOME");
+        xdg_home = getenv("XDG_CONFIG_HOME");
+        unsetenv("HOME");
+        unsetenv("XDG_CONFIG_HOME");
         result = write_archive(argv.argc, nargv, NULL, 1, NULL, 0);
+        if (user_home)
+                setenv("HOME", user_home, 1);
+        if (xdg_home)
+                setenv("XDG_CONFIG_HOME", xdg_home, 1);
         argv_array_clear(&argv);
         free(nargv);
         return result;