From 8ed85ef3de9cdeee86e281a8b46be1bd49a36e7a Mon Sep 17 00:00:00 2001
From: Werner Koch <wk@gnupg.org>
Date: Wed, 9 Sep 2020 20:33:06 +0200
Subject: [PATCH] agent: Keep some permissions of private-keys-v1.d.

* common/sysutils.c (modestr_to_mode): Re-implement.
(gnupg_chmod): Support keeping of permissions.
--

GnuPG-bug-id: 2312
---
 agent/gpg-agent.c | 16 +++++++++---
 common/sysutils.c | 64 ++++++++++++++++++++++++++++++-----------------
 2 files changed, 54 insertions(+), 26 deletions(-)

diff --git a/agent/gpg-agent.c b/agent/gpg-agent.c
index bbad80074..f167c96db 100644
--- a/agent/gpg-agent.c
+++ b/agent/gpg-agent.c
@@ -2273,10 +2273,20 @@ create_private_keys_directory (const char *home)
                    fname, strerror (errno) );
       else if (!opt.quiet)
         log_info (_("directory '%s' created\n"), fname);
+
+      if (gnupg_chmod (fname, "-rwx"))
+        log_error (_("can't set permissions of '%s': %s\n"),
+                   fname, strerror (errno));
+    }
+  else
+    {
+      /* The file exists or another error.  Make sure we have sensible
+       * permissions.  We enforce rwx for user but keep existing group
+       * permissions.  Permissions for other are always cleared.  */
+      if (gnupg_chmod (fname, "-rwx...---"))
+        log_error (_("can't set permissions of '%s': %s\n"),
+                   fname, strerror (errno));
     }
-  if (gnupg_chmod (fname, "-rwx"))
-    log_error (_("can't set permissions of '%s': %s\n"),
-               fname, strerror (errno));
   xfree (fname);
 }
 
diff --git a/common/sysutils.c b/common/sysutils.c
index efc2dfe9b..140d1d7be 100644
--- a/common/sysutils.c
+++ b/common/sysutils.c
@@ -749,33 +749,38 @@ gnupg_rename_file (const char *oldname, const char *newname, int *block_signals)
 
 #ifndef HAVE_W32_SYSTEM
 static mode_t
-modestr_to_mode (const char *modestr)
+modestr_to_mode (const char *modestr, mode_t oldmode)
 {
+  static struct {
+    char letter;
+    mode_t value;
+  } table[] = { { '-', 0 },
+                { 'r', S_IRUSR }, { 'w', S_IWUSR }, { 'x', S_IXUSR },
+                { 'r', S_IRGRP }, { 'w', S_IWGRP }, { 'x', S_IXGRP },
+                { 'r', S_IROTH }, { 'w', S_IWOTH }, { 'x', S_IXOTH } };
+  int idx;
   mode_t mode = 0;
 
-  if (modestr && *modestr)
+  /* For now we only support a string as used by ls(1) and no octal
+   * numbers.  The first character must be a dash.  */
+  for (idx=0; idx < 10 && *modestr; idx++, modestr++)
     {
-      modestr++;
-      if (*modestr && *modestr++ == 'r')
-        mode |= S_IRUSR;
-      if (*modestr && *modestr++ == 'w')
-        mode |= S_IWUSR;
-      if (*modestr && *modestr++ == 'x')
-        mode |= S_IXUSR;
-      if (*modestr && *modestr++ == 'r')
-        mode |= S_IRGRP;
-      if (*modestr && *modestr++ == 'w')
-        mode |= S_IWGRP;
-      if (*modestr && *modestr++ == 'x')
-        mode |= S_IXGRP;
-      if (*modestr && *modestr++ == 'r')
-        mode |= S_IROTH;
-      if (*modestr && *modestr++ == 'w')
-        mode |= S_IWOTH;
-      if (*modestr && *modestr++ == 'x')
-        mode |= S_IXOTH;
+      if (*modestr == table[idx].letter)
+        mode |= table[idx].value;
+      else if (*modestr == '.')
+        {
+          if (!idx)
+            ;  /* Skip the dummy.  */
+          else if ((oldmode & table[idx].value))
+            mode |= (oldmode & table[idx].value);
+          else
+            mode &= ~(oldmode & table[idx].value);
+        }
+      else if (*modestr != '-')
+        break;
     }
 
+
   return mode;
 }
 #endif
@@ -815,7 +820,8 @@ gnupg_chdir (const char *name)
 /* A wrapper around chmod which takes a string for the mode argument.
    This makes it easier to handle the mode argument which is not
    defined on all systems.  The format of the modestring is the same
-   as for gnupg_mkdir.  */
+   as for gnupg_mkdir with extra feature that a '.' keeps the original
+   mode bit.  */
 int
 gnupg_chmod (const char *name, const char *modestr)
 {
@@ -824,7 +830,19 @@ gnupg_chmod (const char *name, const char *modestr)
   (void)modestr;
   return 0;
 #else
-  return chmod (name, modestr_to_mode (modestr));
+  mode_t oldmode;
+  if (strchr (modestr, '.'))
+    {
+      /* Get the old mode so that a '.' can copy that bit.  */
+      struct stat st;
+
+      if (stat (name, &st))
+        return -1;
+      oldmode = st.st_mode;
+    }
+  else
+    oldmode = 0;
+  return chmod (name, modestr_to_mode (modestr, oldmode));
 #endif
 }