[PATCH 0/3] Provide a useful default user ident on Windows

[PATCH 0/3] Provide a useful default user ident on Windows

[Johannes Schindelin via GitGitGadget]

On Linux, we use the gecos information to come up with a sensible user
name/email. On Windows, there is no gecos. But there is something
comparable, and with these patches, we use it.

This has been carried in Git for Windows for three years, and is considered
mature.

Johannes Schindelin (3):
  getpwuid(mingw): initialize the structure only once
  getpwuid(mingw): provide a better default for the user name
  mingw: use domain information for default email

 compat/mingw.c    | 60 +++++++++++++++++++++++++++++++++++++++++------
 compat/mingw.h    |  2 ++
 git-compat-util.h |  4 ++++
 ident.c           |  3 +++
 4 files changed, 62 insertions(+), 7 deletions(-)


base-commit: 5a0cc8aca797dbd7d2be3b67458ff880ed45cddf
Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-45%2Fdscho%2Fdefault-ident-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-45/dscho/default-ident-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/45
-- 
gitgitgadget

[PATCH 1/3] getpwuid(mingw): initialize the structure only once

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 compat/mingw.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/compat/mingw.c b/compat/mingw.c
index 18caf21969..597781b370 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1800,16 +1800,27 @@ int mingw_getpagesize(void)
 
 struct passwd *getpwuid(int uid)
 {
+	static unsigned initialized;
 	static char user_name[100];
-	static struct passwd p;
+	static struct passwd *p;
+	DWORD len;
 
-	DWORD len = sizeof(user_name);
-	if (!GetUserName(user_name, &len))
+	if (initialized)
+		return p;
+
+	len = sizeof(user_name);
+	if (!GetUserName(user_name, &len)) {
+		initialized = 1;
 		return NULL;
-	p.pw_name = user_name;
-	p.pw_gecos = "unknown";
-	p.pw_dir = NULL;
-	return &p;
+	}
+
+	p = xmalloc(sizeof(*p));
+	p->pw_name = user_name;
+	p->pw_gecos = "unknown";
+	p->pw_dir = NULL;
+
+	initialized = 1;
+	return p;
 }
 
 static HANDLE timer_event;
-- 
gitgitgadget

Re: [PATCH 1/3] getpwuid(mingw): initialize the structure only once

[Eric Sunshine]

On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
<gitgitgadget@gmail.com> wrote:
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
> diff --git a/compat/mingw.c b/compat/mingw.c
> @@ -1800,16 +1800,27 @@ int mingw_getpagesize(void)
>  struct passwd *getpwuid(int uid)
>  {
> +       static unsigned initialized;
>         static char user_name[100];
> -       static struct passwd p;
> +       static struct passwd *p;
>
> +       if (initialized)
> +               return p;
> +
> +       len = sizeof(user_name);
> +       if (!GetUserName(user_name, &len)) {
> +               initialized = 1;
>                 return NULL;
> +       }

If GetUserName() fails, that failure is recorded (as "initialized=1"
and 'p' is still NULL), so subsequent invocations just return NULL
without doing any more work. Makes sense.

> +       p = xmalloc(sizeof(*p));
> +       p->pw_name = user_name;
> +       p->pw_gecos = "unknown";
> +       p->pw_dir = NULL;
> +
> +       initialized = 1;
> +       return p;
>  }

[PATCH 2/3] getpwuid(mingw): provide a better default for the user name

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

We do have the excellent GetUserInfoEx() function to obtain more
detailed information of the current user (if the user is part of a
Windows domain); Let's use it.

Suggested by Lutz Roeder.

To avoid the cost of loading Secur32.dll (even lazily, loading DLLs
takes a non-neglibile amount of time), we use the established technique
to load DLLs only when, and if, needed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 compat/mingw.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/compat/mingw.c b/compat/mingw.c
index 597781b370..623ff5daf5 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -5,6 +5,7 @@
 #include "../strbuf.h"
 #include "../run-command.h"
 #include "../cache.h"
+#include "win32/lazyload.h"
 
 #define HCAST(type, handle) ((type)(intptr_t)handle)
 
@@ -1798,6 +1799,33 @@ int mingw_getpagesize(void)
 	return si.dwAllocationGranularity;
 }
 
+/* See https://msdn.microsoft.com/en-us/library/windows/desktop/ms724435.aspx */
+enum EXTENDED_NAME_FORMAT {
+	NameDisplay = 3,
+	NameUserPrincipal = 8
+};
+
+static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
+{
+	DECLARE_PROC_ADDR(secur32.dll, BOOL, GetUserNameExW,
+		enum EXTENDED_NAME_FORMAT, LPCWSTR, PULONG);
+	static wchar_t wbuffer[1024];
+	DWORD len;
+
+	if (!INIT_PROC_ADDR(GetUserNameExW))
+		return NULL;
+
+	len = ARRAY_SIZE(wbuffer);
+	if (GetUserNameExW(type, wbuffer, &len)) {
+		char *converted = xmalloc((len *= 3));
+		if (xwcstoutf(converted, wbuffer, len) >= 0)
+			return converted;
+		free(converted);
+	}
+
+	return NULL;
+}
+
 struct passwd *getpwuid(int uid)
 {
 	static unsigned initialized;
@@ -1816,7 +1844,9 @@ struct passwd *getpwuid(int uid)
 
 	p = xmalloc(sizeof(*p));
 	p->pw_name = user_name;
-	p->pw_gecos = "unknown";
+	p->pw_gecos = get_extended_user_info(NameDisplay);
+	if (!p->pw_gecos)
+		p->pw_gecos = "unknown";
 	p->pw_dir = NULL;
 
 	initialized = 1;
-- 
gitgitgadget

Re: [PATCH 2/3] getpwuid(mingw): provide a better default for the user name

[Eric Sunshine]

On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
<gitgitgadget@gmail.com> wrote:
> We do have the excellent GetUserInfoEx() function to obtain more
> detailed information of the current user (if the user is part of a
> Windows domain); Let's use it.
> [...]
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
> diff --git a/compat/mingw.c b/compat/mingw.c
> @@ -1798,6 +1799,33 @@ int mingw_getpagesize(void)
> +static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
> +{
> +       DECLARE_PROC_ADDR(secur32.dll, BOOL, GetUserNameExW,
> +               enum EXTENDED_NAME_FORMAT, LPCWSTR, PULONG);
> +       static wchar_t wbuffer[1024];

Does this need to be static? It's not being returned to the caller.

> +       len = ARRAY_SIZE(wbuffer);
> +       if (GetUserNameExW(type, wbuffer, &len)) {
> +               char *converted = xmalloc((len *= 3));
> +               if (xwcstoutf(converted, wbuffer, len) >= 0)
> +                       return converted;
> +               free(converted);
> +       }

If xwcstoutf() fails, 'converted' is freed; otherwise, the allocated
'converted' is stored in the caller's statically held 'passwd' struct.
Okay.

> +       return NULL;
> +}

Re: [PATCH 2/3] getpwuid(mingw): provide a better default for the user name

[Johannes Schindelin]

Hi Eric,

On Mon, 15 Oct 2018, Eric Sunshine wrote:

> On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> > We do have the excellent GetUserInfoEx() function to obtain more
> > detailed information of the current user (if the user is part of a
> > Windows domain); Let's use it.
> > [...]
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> > diff --git a/compat/mingw.c b/compat/mingw.c
> > @@ -1798,6 +1799,33 @@ int mingw_getpagesize(void)
> > +static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
> > +{
> > +       DECLARE_PROC_ADDR(secur32.dll, BOOL, GetUserNameExW,
> > +               enum EXTENDED_NAME_FORMAT, LPCWSTR, PULONG);
> > +       static wchar_t wbuffer[1024];
> 
> Does this need to be static? It's not being returned to the caller.

It does not. Fixed.

> > +       len = ARRAY_SIZE(wbuffer);
> > +       if (GetUserNameExW(type, wbuffer, &len)) {
> > +               char *converted = xmalloc((len *= 3));

Oh wow. I *just* realized this. It is an off-by-one: the `xmalloc()` call
needs to receive `len + 1` to accommodate for the trailing NUL. Will fix,
too.

Ciao,
Dscho

> > +               if (xwcstoutf(converted, wbuffer, len) >= 0)
> > +                       return converted;
> > +               free(converted);
> > +       }
> 
> If xwcstoutf() fails, 'converted' is freed; otherwise, the allocated
> 'converted' is stored in the caller's statically held 'passwd' struct.
> Okay.
> 
> > +       return NULL;
> > +}
> 

Re: [PATCH 2/3] getpwuid(mingw): provide a better default for the user name

[Eric Sunshine]

On Tue, Oct 16, 2018 at 8:38 AM Johannes Schindelin
<Johannes.Schindelin@gmx.de> wrote:
> On Mon, 15 Oct 2018, Eric Sunshine wrote:
> > On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
> > <gitgitgadget@gmail.com> wrote:
> > > +       len = ARRAY_SIZE(wbuffer);
> > > +       if (GetUserNameExW(type, wbuffer, &len)) {
> > > +               char *converted = xmalloc((len *= 3));
>
> Oh wow. I *just* realized this. It is an off-by-one: the `xmalloc()` call
> needs to receive `len + 1` to accommodate for the trailing NUL. Will fix,
> too.

Or, xmallocz() (note the "z") which gives you overflow-checking of the
+1 for free.

Re: [PATCH 2/3] getpwuid(mingw): provide a better default for the user name

[Johannes Schindelin]

Hi Eric,

On Tue, 16 Oct 2018, Eric Sunshine wrote:

> On Tue, Oct 16, 2018 at 8:38 AM Johannes Schindelin
> <Johannes.Schindelin@gmx.de> wrote:
> > On Mon, 15 Oct 2018, Eric Sunshine wrote:
> > > On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
> > > <gitgitgadget@gmail.com> wrote:
> > > > +       len = ARRAY_SIZE(wbuffer);
> > > > +       if (GetUserNameExW(type, wbuffer, &len)) {
> > > > +               char *converted = xmalloc((len *= 3));
> >
> > Oh wow. I *just* realized this. It is an off-by-one: the `xmalloc()` call
> > needs to receive `len + 1` to accommodate for the trailing NUL. Will fix,
> > too.
> 
> Or, xmallocz() (note the "z") which gives you overflow-checking of the
> +1 for free.

Very good point! Thanks for the suggestion,
Dscho

[PATCH 3/3] mingw: use domain information for default email

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

When a user is registered in a Windows domain, it is really easy to
obtain the email address. So let's do that.

Suggested by Lutz Roeder.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 compat/mingw.c    | 5 +++++
 compat/mingw.h    | 2 ++
 git-compat-util.h | 4 ++++
 ident.c           | 3 +++
 4 files changed, 14 insertions(+)

diff --git a/compat/mingw.c b/compat/mingw.c
index 623ff5daf5..44264fe3fd 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1826,6 +1826,11 @@ static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
 	return NULL;
 }
 
+char *mingw_query_user_email(void)
+{
+	return get_extended_user_info(NameUserPrincipal);
+}
+
 struct passwd *getpwuid(int uid)
 {
 	static unsigned initialized;
diff --git a/compat/mingw.h b/compat/mingw.h
index 571019d0bd..f31dcff2be 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -424,6 +424,8 @@ static inline void convert_slashes(char *path)
 int mingw_offset_1st_component(const char *path);
 #define offset_1st_component mingw_offset_1st_component
 #define PATH_SEP ';'
+extern char *mingw_query_user_email(void);
+#define query_user_email mingw_query_user_email
 #if !defined(__MINGW64_VERSION_MAJOR) && (!defined(_MSC_VER) || _MSC_VER < 1800)
 #define PRIuMAX "I64u"
 #define PRId64 "I64d"
diff --git a/git-compat-util.h b/git-compat-util.h
index 5f2e90932f..71779cb0ae 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -382,6 +382,10 @@ static inline char *git_find_last_dir_sep(const char *path)
 #define find_last_dir_sep git_find_last_dir_sep
 #endif
 
+#ifndef query_user_email
+#define query_user_email() NULL
+#endif
+
 #if defined(__HP_cc) && (__HP_cc >= 61000)
 #define NORETURN __attribute__((noreturn))
 #define NORETURN_PTR
diff --git a/ident.c b/ident.c
index 327abe557f..33bcf40644 100644
--- a/ident.c
+++ b/ident.c
@@ -168,6 +168,9 @@ const char *ident_default_email(void)
 			strbuf_addstr(&git_default_email, email);
 			committer_ident_explicitly_given |= IDENT_MAIL_GIVEN;
 			author_ident_explicitly_given |= IDENT_MAIL_GIVEN;
+		} else if ((email = query_user_email()) && email[0]) {
+			strbuf_addstr(&git_default_email, email);
+			free((char *)email);
 		} else
 			copy_email(xgetpwuid_self(&default_email_is_bogus),
 				   &git_default_email, &default_email_is_bogus);
-- 
gitgitgadget

Re: [PATCH 3/3] mingw: use domain information for default email

[Eric Sunshine]

On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
<gitgitgadget@gmail.com> wrote:
> When a user is registered in a Windows domain, it is really easy to
> obtain the email address. So let's do that.
> [...]
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
> diff --git a/compat/mingw.c b/compat/mingw.c
> @@ -1826,6 +1826,11 @@ static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
> +char *mingw_query_user_email(void)
> +{
> +       return get_extended_user_info(NameUserPrincipal);
> +}
> diff --git a/ident.c b/ident.c
> @@ -168,6 +168,9 @@ const char *ident_default_email(void)
> +               } else if ((email = query_user_email()) && email[0]) {
> +                       strbuf_addstr(&git_default_email, email);
> +                       free((char *)email);

If query_user_email(), which calls get_extended_user_info(), returns
NULL, then we do nothing (and don't worry about freeing the result).
However, if query_user_email() returns a zero-length allocated string,
then this conditional will leak that string (due to the email[0]
check). From patch 2/3, we see in get_extended_user_info():

+static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
+{
+       if (GetUserNameExW(type, wbuffer, &len)) {
+               char *converted = xmalloc((len *= 3));
+               if (xwcstoutf(converted, wbuffer, len) >= 0)
+                       return converted;

that it may possibly return a zero-length string (due to the ">=0").
Do we care about this potential leak (or is GetUserNameExW()
guaranteed never to return such a string)?

Re: [PATCH 3/3] mingw: use domain information for default email

[Johannes Schindelin]

Hi Eric,

On Mon, 15 Oct 2018, Eric Sunshine wrote:

> On Mon, Oct 15, 2018 at 5:47 AM Johannes Schindelin via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> > When a user is registered in a Windows domain, it is really easy to
> > obtain the email address. So let's do that.
> > [...]
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> > diff --git a/compat/mingw.c b/compat/mingw.c
> > @@ -1826,6 +1826,11 @@ static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
> > +char *mingw_query_user_email(void)
> > +{
> > +       return get_extended_user_info(NameUserPrincipal);
> > +}
> > diff --git a/ident.c b/ident.c
> > @@ -168,6 +168,9 @@ const char *ident_default_email(void)
> > +               } else if ((email = query_user_email()) && email[0]) {
> > +                       strbuf_addstr(&git_default_email, email);
> > +                       free((char *)email);
> 
> If query_user_email(), which calls get_extended_user_info(), returns
> NULL, then we do nothing (and don't worry about freeing the result).
> However, if query_user_email() returns a zero-length allocated string,
> then this conditional will leak that string (due to the email[0]
> check). From patch 2/3, we see in get_extended_user_info():
> 
> +static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
> +{
> +       if (GetUserNameExW(type, wbuffer, &len)) {
> +               char *converted = xmalloc((len *= 3));
> +               if (xwcstoutf(converted, wbuffer, len) >= 0)
> +                       return converted;
> 
> that it may possibly return a zero-length string (due to the ">=0").
> Do we care about this potential leak (or is GetUserNameExW()
> guaranteed never to return such a string)?

Quite honestly, I think that this is so rare an instance (if it *can*
happen at all) that I simply don't care ;-)

Ciao,
Dscho

Re: [PATCH 3/3] mingw: use domain information for default email

[Junio C Hamano]

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> +char *mingw_query_user_email(void)
> +{
> +	return get_extended_user_info(NameUserPrincipal);
> +}
> +
> ...
>  
> +#ifndef query_user_email
> +#define query_user_email() NULL
> +#endif

The three patches look sensible to me; will queue.

You may already have audited our use of "struct passwd",
"getpwnam()" and "getpwuid()"--I haven't.  I think we use these only
to learn user's email (to be used as the default ident) and home
directory (to expand "git config --type=path").  If that is really
the case, it may be a worthwhile clean-up to introduce our own API
that offers these two exact functions, have the per-platform
implementation of the API in compat/, and get rid of "struct passwd"
and calls to getpw*() functions out of the core Git proper, to wean
ourselves away from depending on POSIX too much.

But of course that is a separate topic.