Allow deriving the current user's home directory via the HOME variable

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`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
This commit is contained in:
Johannes Schindelin 2023-03-28 10:17:14 +02:00 committed by Corinna Vinschen
parent fc6e89c937
commit 27376c60a9
3 changed files with 75 additions and 1 deletions

View File

@ -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;

View File

@ -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)

View File

@ -1203,6 +1203,17 @@ 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>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 <term><literal>windows</literal></term> schema at the
expense of determining only the current user's home directory
correctly. This schema is skipped for any other account.
</listitem>
</varlistentry>
</variablelist>
<para>
@ -1335,6 +1346,17 @@ 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 <term><literal>windows</literal></term> 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