[PATCH v6 1/4] Allow deriving the current user's home directory via the HOME variable
Johannes Schindelin
johannes.schindelin@gmx.de
Tue Apr 4 15:07:45 GMT 2023
This patch hails from Git for Windows (where the Cygwin runtime is used
in the form of a slightly modified MSYS2 runtime), where it is a
well-established technique to let the `$HOME` variable define where the
current user's home directory is, falling back to `$HOMEDRIVE$HOMEPATH`
and `$USERPROFILE`.
The idea is that we want to share user-specific settings between
programs, whether they be Cygwin, MSYS2 or not. Unfortunately, we
cannot blindly activate the "db_home: windows" setting because in some
setups, the user's home directory is set to a hidden directory via an
UNC path (\\share\some\hidden\folder$) -- something many programs
cannot handle correctly, e.g. `cmd.exe` and other native Windows
applications that users want to employ as Git helpers.
The established technique is to allow setting the user's home directory
via the environment variables mentioned above: `$HOMEDRIVE$HOMEPATH` or
`$USERPROFILE`. This has the additional advantage that it is much
faster than querying the Windows user database.
Of course this scheme needs to be opt-in. For that reason, it needs
to be activated explicitly via `db_home: env` in `/etc/nsswitch.conf`.
Documentation-fixes-by: Corinna Vinschen <corinna@vinschen.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
winsup/cygwin/local_includes/cygheap.h | 3 +-
winsup/cygwin/uinfo.cc | 51 ++++++++++++++++++++++++++
winsup/doc/ntsec.xml | 20 +++++++++-
3 files changed, 72 insertions(+), 2 deletions(-)
diff --git a/winsup/cygwin/local_includes/cygheap.h b/winsup/cygwin/local_includes/cygheap.h
index d885ca1230..b6acdf7f18 100644
--- a/winsup/cygwin/local_includes/cygheap.h
+++ b/winsup/cygwin/local_includes/cygheap.h
@@ -358,7 +358,8 @@ public:
NSS_SCHEME_UNIX,
NSS_SCHEME_DESC,
NSS_SCHEME_PATH,
- NSS_SCHEME_FREEATTR
+ NSS_SCHEME_FREEATTR,
+ NSS_SCHEME_ENV
};
struct nss_scheme_t {
nss_scheme_method method;
diff --git a/winsup/cygwin/uinfo.cc b/winsup/cygwin/uinfo.cc
index 30df6db6d8..baa670478d 100644
--- a/winsup/cygwin/uinfo.cc
+++ b/winsup/cygwin/uinfo.cc
@@ -733,6 +733,8 @@ cygheap_pwdgrp::nss_init_line (const char *line)
scheme[idx].method = NSS_SCHEME_UNIX;
else if (NSS_CMP ("desc"))
scheme[idx].method = NSS_SCHEME_DESC;
+ else if (NSS_CMP ("env"))
+ scheme[idx].method = NSS_SCHEME_ENV;
else if (NSS_NCMP ("/"))
{
const char *e = c + strcspn (c, " \t");
@@ -921,6 +923,42 @@ fetch_from_path (cyg_ldap *pldap, PUSER_INFO_3 ui, cygpsid &sid, PCWSTR str,
return ret;
}
+static char *
+fetch_home_env (void)
+{
+ /* If `HOME` is set, prefer it */
+ const char *home = getenv ("HOME");
+ if (home)
+ return strdup (home);
+
+ /* If `HOME` is unset, fall back to `HOMEDRIVE``HOMEPATH`
+ (without a directory separator, as `HOMEPATH` starts with one). */
+ const char *home_drive = getenv ("HOMEDRIVE");
+ if (home_drive)
+ {
+ const char *home_path = getenv ("HOMEPATH");
+ if (home_path)
+ {
+ tmp_pathbuf tp;
+ char *p = tp.c_get (), *q;
+
+ // concatenate HOMEDRIVE and HOMEPATH
+ q = stpncpy (p, home_drive, NT_MAX_PATH);
+ strlcpy (q, home_path, NT_MAX_PATH - (q - p));
+ return (char *) cygwin_create_path (CCP_WIN_A_TO_POSIX, p);
+ }
+ }
+
+ /* If neither `HOME` nor `HOMEDRIVE``HOMEPATH` are set, fall back
+ to `USERPROFILE`; In corporate setups, this might point to a
+ disconnected network share, hence this is the last fall back. */
+ home = getenv ("USERPROFILE");
+ if (home)
+ return (char *) cygwin_create_path (CCP_WIN_A_TO_POSIX, home);
+
+ return NULL;
+}
+
char *
cygheap_pwdgrp::get_home (cyg_ldap *pldap, cygpsid &sid, PCWSTR dom,
PCWSTR dnsdomain, PCWSTR name, bool full_qualified)
@@ -980,6 +1018,10 @@ cygheap_pwdgrp::get_home (cyg_ldap *pldap, cygpsid &sid, PCWSTR dom,
}
}
break;
+ case NSS_SCHEME_ENV:
+ if (RtlEqualSid (sid, cygheap->user.sid ()))
+ home = fetch_home_env ();
+ break;
}
}
return home;
@@ -1012,6 +1054,10 @@ cygheap_pwdgrp::get_home (PUSER_INFO_3 ui, cygpsid &sid, PCWSTR dom,
home = fetch_from_path (NULL, ui, sid, home_scheme[idx].attrib,
dom, NULL, name, full_qualified);
break;
+ case NSS_SCHEME_ENV:
+ if (RtlEqualSid (sid, cygheap->user.sid ()))
+ home = fetch_home_env ();
+ break;
}
}
return home;
@@ -1031,6 +1077,7 @@ cygheap_pwdgrp::get_shell (cyg_ldap *pldap, cygpsid &sid, PCWSTR dom,
case NSS_SCHEME_FALLBACK:
return NULL;
case NSS_SCHEME_WINDOWS:
+ case NSS_SCHEME_ENV:
break;
case NSS_SCHEME_CYGWIN:
if (pldap->fetch_ad_account (sid, false, dnsdomain))
@@ -1095,6 +1142,7 @@ cygheap_pwdgrp::get_shell (PUSER_INFO_3 ui, cygpsid &sid, PCWSTR dom,
case NSS_SCHEME_CYGWIN:
case NSS_SCHEME_UNIX:
case NSS_SCHEME_FREEATTR:
+ case NSS_SCHEME_ENV:
break;
case NSS_SCHEME_DESC:
if (ui)
@@ -1176,6 +1224,8 @@ cygheap_pwdgrp::get_gecos (cyg_ldap *pldap, cygpsid &sid, PCWSTR dom,
sys_wcstombs_alloc (&gecos, HEAP_NOTHEAP, val);
}
break;
+ case NSS_SCHEME_ENV:
+ break;
}
}
if (gecos)
@@ -1202,6 +1252,7 @@ cygheap_pwdgrp::get_gecos (PUSER_INFO_3 ui, cygpsid &sid, PCWSTR dom,
case NSS_SCHEME_CYGWIN:
case NSS_SCHEME_UNIX:
case NSS_SCHEME_FREEATTR:
+ case NSS_SCHEME_ENV:
break;
case NSS_SCHEME_DESC:
if (ui)
diff --git a/winsup/doc/ntsec.xml b/winsup/doc/ntsec.xml
index c6871ecf05..687789076c 100644
--- a/winsup/doc/ntsec.xml
+++ b/winsup/doc/ntsec.xml
@@ -1167,7 +1167,7 @@ and on non-AD machines.
</para>
<para>
-Four schemata are predefined, two schemata are variable. The predefined
+Five schemata are predefined, two schemata are variable. The predefined
schemata are the following:
</para>
@@ -1203,6 +1203,13 @@ schemata are the following:
See <xref linkend="ntsec-mapping-nsswitch-desc"></xref>
for a more detailed description.</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>env</literal></term>
+ <listitem>Utilizes the user's environment. This schema is only supported
+ for setting the home directory yet.
+ See <xref linkend="ntsec-mapping-nsswitch-home"></xref> for
+ the description.</listitem>
+ </varlistentry>
</variablelist>
<para>
@@ -1335,6 +1342,17 @@ of each schema when used with <literal>db_home:</literal>
See <xref linkend="ntsec-mapping-nsswitch-desc"></xref>
for a detailed description.</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>env</literal></term>
+ <listitem>Derives the home directory of the current user from the
+ environment variable <literal>HOME</literal> (falling back to
+ <literal>HOMEDRIVE\HOMEPATH</literal> and
+ <literal>USERPROFILE</literal>, in that order). This is faster
+ than the <literal>windows</literal> schema at the
+ expense of determining only the current user's home directory
+ correctly. This schema is skipped for any other account.
+ </listitem>
+ </varlistentry>
<varlistentry>
<term><literal>@ad_attribute</literal></term>
<listitem>AD only: The user's home directory is set to the path given
--
2.40.0.windows.1
More information about the Cygwin-patches
mailing list