[PATCH v2 2/2] wincred: improve compatibility with windows versions

[Karsten Blees <karsten.blees@gmail.com>]

On WinXP, the windows credential helper doesn't work at all (due to missing
Cred[Un]PackAuthenticationBuffer APIs). On Win7, the credential format used
by wincred is incompatible with native Windows tools (such as the control
panel applet or 'cmdkey.exe /generic'). These Windows tools only set the
TargetName, UserName and CredentialBlob members of the CREDENTIAL
structure (where CredentialBlob is the UTF-16-encoded password).

Remove the unnecessary packing / unpacking of the password, along with the
related API definitions, for compatibility with Windows XP.

Don't use CREDENTIAL_ATTRIBUTEs to identify credentials for compatibility
with Windows credential manager tools. Parse the protocol, username, host
and path fields from the credential's target name instead.

Credentials created with an old wincred version will have mangled or empty
passwords after this change.

Signed-off-by: Karsten Blees <blees@dcon.de>
---
 .../credential/wincred/git-credential-wincred.c    | 199 ++++++++-------------
 1 file changed, 70 insertions(+), 129 deletions(-)

diff --git a/contrib/credential/wincred/git-credential-wincred.c b/contrib/credential/wincred/git-credential-wincred.c
index 94d7140..dac19ea 100644
--- a/contrib/credential/wincred/git-credential-wincred.c
+++ b/contrib/credential/wincred/git-credential-wincred.c
@@ -9,6 +9,8 @@
 
 /* common helpers */
 
+#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
+
 static void die(const char *err, ...)
 {
 	char msg[4096];
@@ -30,14 +32,6 @@ static void *xmalloc(size_t size)
 	return ret;
 }
 
-static char *xstrdup(const char *str)
-{
-	char *ret = strdup(str);
-	if (!ret)
-		die("Out of memory");
-	return ret;
-}
-
 /* MinGW doesn't have wincred.h, so we need to define stuff */
 
 typedef struct _CREDENTIAL_ATTRIBUTEW {
@@ -67,20 +61,14 @@ typedef struct _CREDENTIALW {
 #define CRED_MAX_ATTRIBUTES 64
 
 typedef BOOL (WINAPI *CredWriteWT)(PCREDENTIALW, DWORD);
-typedef BOOL (WINAPI *CredUnPackAuthenticationBufferWT)(DWORD, PVOID, DWORD,
-    LPWSTR, DWORD *, LPWSTR, DWORD *, LPWSTR, DWORD *);
 typedef BOOL (WINAPI *CredEnumerateWT)(LPCWSTR, DWORD, DWORD *,
     PCREDENTIALW **);
-typedef BOOL (WINAPI *CredPackAuthenticationBufferWT)(DWORD, LPWSTR, LPWSTR,
-    PBYTE, DWORD *);
 typedef VOID (WINAPI *CredFreeT)(PVOID);
 typedef BOOL (WINAPI *CredDeleteWT)(LPCWSTR, DWORD, DWORD);
 
-static HMODULE advapi, credui;
+static HMODULE advapi;
 static CredWriteWT CredWriteW;
-static CredUnPackAuthenticationBufferWT CredUnPackAuthenticationBufferW;
 static CredEnumerateWT CredEnumerateW;
-static CredPackAuthenticationBufferWT CredPackAuthenticationBufferW;
 static CredFreeT CredFree;
 static CredDeleteWT CredDeleteW;
 
@@ -88,74 +76,84 @@ static void load_cred_funcs(void)
 {
 	/* load DLLs */
 	advapi = LoadLibrary("advapi32.dll");
-	credui = LoadLibrary("credui.dll");
-	if (!advapi || !credui)
-		die("failed to load DLLs");
+	if (!advapi)
+		die("failed to load advapi32.dll");
 
 	/* get function pointers */
 	CredWriteW = (CredWriteWT)GetProcAddress(advapi, "CredWriteW");
-	CredUnPackAuthenticationBufferW = (CredUnPackAuthenticationBufferWT)
-	    GetProcAddress(credui, "CredUnPackAuthenticationBufferW");
 	CredEnumerateW = (CredEnumerateWT)GetProcAddress(advapi,
 	    "CredEnumerateW");
-	CredPackAuthenticationBufferW = (CredPackAuthenticationBufferWT)
-	    GetProcAddress(credui, "CredPackAuthenticationBufferW");
 	CredFree = (CredFreeT)GetProcAddress(advapi, "CredFree");
 	CredDeleteW = (CredDeleteWT)GetProcAddress(advapi, "CredDeleteW");
-	if (!CredWriteW || !CredUnPackAuthenticationBufferW ||
-	    !CredEnumerateW || !CredPackAuthenticationBufferW || !CredFree ||
-	    !CredDeleteW)
+	if (!CredWriteW || !CredEnumerateW || !CredFree || !CredDeleteW)
 		die("failed to load functions");
 }
 
-static char target_buf[1024];
-static char *protocol, *host, *path, *username;
-static WCHAR *wusername, *password, *target;
+static WCHAR *wusername, *password, *protocol, *host, *path, target[1024];
 
-static void write_item(const char *what, WCHAR *wbuf)
+static void write_item(const char *what, LPCWSTR wbuf, int wlen)
 {
 	char *buf;
-	int len = WideCharToMultiByte(CP_UTF8, 0, wbuf, -1, NULL, 0, NULL,
+	int len = WideCharToMultiByte(CP_UTF8, 0, wbuf, wlen, NULL, 0, NULL,
 	    FALSE);
 	buf = xmalloc(len);
 
-	if (!WideCharToMultiByte(CP_UTF8, 0, wbuf, -1, buf, len, NULL, FALSE))
+	if (!WideCharToMultiByte(CP_UTF8, 0, wbuf, wlen, buf, len, NULL, FALSE))
 		die("WideCharToMultiByte failed!");
 
 	printf("%s=", what);
-	fwrite(buf, 1, len - 1, stdout);
+	fwrite(buf, 1, len, stdout);
 	putchar('\n');
 	free(buf);
 }
 
-static int match_attr(const CREDENTIALW *cred, const WCHAR *keyword,
-    const char *want)
+/*
+ * Match an (optional) expected string and a delimiter in the target string,
+ * consuming the matched text by updating the target pointer.
+ */
+static int match_part(LPCWSTR *ptarget, LPCWSTR want, LPCWSTR delim)
 {
-	int i;
-	if (!want)
-		return 1;
-
-	for (i = 0; i < cred->AttributeCount; ++i)
-		if (!wcscmp(cred->Attributes[i].Keyword, keyword))
-			return !strcmp((const char *)cred->Attributes[i].Value,
-			    want);
-
-	return 0; /* not found */
+	LPCWSTR delim_pos, start = *ptarget;
+	int len;
+
+	/* find start of delimiter (or end-of-string if delim is empty) */
+	if (*delim)
+		delim_pos = wcsstr(start, delim);
+	else
+		delim_pos = start + wcslen(start);
+
+	/*
+	 * match text up to delimiter, or end of string (e.g. the '/' after
+	 * host is optional if not followed by a path)
+	 */
+	if (delim_pos)
+		len = delim_pos - start;
+	else
+		len = wcslen(start);
+
+	/* update ptarget if we either found a delimiter or need a match */
+	if (delim_pos || want)
+		*ptarget = delim_pos ? delim_pos + wcslen(delim) : start + len;
+
+	return !want || (!wcsncmp(want, start, len) && !want[len]);
 }
 
 static int match_cred(const CREDENTIALW *cred)
 {
-	return (!wusername || !wcscmp(wusername, cred->UserName)) &&
-	    match_attr(cred, L"git_protocol", protocol) &&
-	    match_attr(cred, L"git_host", host) &&
-	    match_attr(cred, L"git_path", path);
+	LPCWSTR target = cred->TargetName;
+	if (wusername && wcscmp(wusername, cred->UserName))
+		return 0;
+
+	return match_part(&target, L"git", L":") &&
+		match_part(&target, protocol, L"://") &&
+		match_part(&target, wusername, L"@") &&
+		match_part(&target, host, L"/") &&
+		match_part(&target, path, L"");
 }
 
 static void get_credential(void)
 {
-	WCHAR *user_buf, *pass_buf;
-	DWORD user_buf_size = 0, pass_buf_size = 0;
-	CREDENTIALW **creds, *cred = NULL;
+	CREDENTIALW **creds;
 	DWORD num_creds;
 	int i;
 
@@ -165,90 +163,36 @@ static void get_credential(void)
 	/* search for the first credential that matches username */
 	for (i = 0; i < num_creds; ++i)
 		if (match_cred(creds[i])) {
-			cred = creds[i];
+			write_item("username", creds[i]->UserName,
+				wcslen(creds[i]->UserName));
+			write_item("password",
+				(LPCWSTR)creds[i]->CredentialBlob,
+				creds[i]->CredentialBlobSize / sizeof(WCHAR));
 			break;
 		}
-	if (!cred)
-		return;
-
-	CredUnPackAuthenticationBufferW(0, cred->CredentialBlob,
-	    cred->CredentialBlobSize, NULL, &user_buf_size, NULL, NULL,
-	    NULL, &pass_buf_size);
-
-	user_buf = xmalloc(user_buf_size * sizeof(WCHAR));
-	pass_buf = xmalloc(pass_buf_size * sizeof(WCHAR));
-
-	if (!CredUnPackAuthenticationBufferW(0, cred->CredentialBlob,
-	    cred->CredentialBlobSize, user_buf, &user_buf_size, NULL, NULL,
-	    pass_buf, &pass_buf_size))
-		die("CredUnPackAuthenticationBuffer failed");
 
 	CredFree(creds);
-
-	/* zero-terminate (sizes include zero-termination) */
-	user_buf[user_buf_size - 1] = L'\0';
-	pass_buf[pass_buf_size - 1] = L'\0';
-
-	write_item("username", user_buf);
-	write_item("password", pass_buf);
-
-	free(user_buf);
-	free(pass_buf);
-}
-
-static void write_attr(CREDENTIAL_ATTRIBUTEW *attr, const WCHAR *keyword,
-    const char *value)
-{
-	attr->Keyword = (LPWSTR)keyword;
-	attr->Flags = 0;
-	attr->ValueSize = strlen(value) + 1; /* store zero-termination */
-	attr->Value = (LPBYTE)value;
 }
 
 static void store_credential(void)
 {
 	CREDENTIALW cred;
-	BYTE *auth_buf;
-	DWORD auth_buf_size = 0;
-	CREDENTIAL_ATTRIBUTEW attrs[CRED_MAX_ATTRIBUTES];
 
 	if (!wusername || !password)
 		return;
 
-	/* query buffer size */
-	CredPackAuthenticationBufferW(0, wusername, password,
-	    NULL, &auth_buf_size);
-
-	auth_buf = xmalloc(auth_buf_size);
-
-	if (!CredPackAuthenticationBufferW(0, wusername, password,
-	    auth_buf, &auth_buf_size))
-		die("CredPackAuthenticationBuffer failed");
-
 	cred.Flags = 0;
 	cred.Type = CRED_TYPE_GENERIC;
 	cred.TargetName = target;
 	cred.Comment = L"saved by git-credential-wincred";
-	cred.CredentialBlobSize = auth_buf_size;
-	cred.CredentialBlob = auth_buf;
+	cred.CredentialBlobSize = (wcslen(password)) * sizeof(WCHAR);
+	cred.CredentialBlob = (LPVOID)password;
 	cred.Persist = CRED_PERSIST_LOCAL_MACHINE;
-	cred.AttributeCount = 1;
-	cred.Attributes = attrs;
+	cred.AttributeCount = 0;
+	cred.Attributes = NULL;
 	cred.TargetAlias = NULL;
 	cred.UserName = wusername;
 
-	write_attr(attrs, L"git_protocol", protocol);
-
-	if (host) {
-		write_attr(attrs + cred.AttributeCount, L"git_host", host);
-		cred.AttributeCount++;
-	}
-
-	if (path) {
-		write_attr(attrs + cred.AttributeCount, L"git_path", path);
-		cred.AttributeCount++;
-	}
-
 	if (!CredWriteW(&cred, 0))
 		die("CredWrite failed");
 }
@@ -298,13 +242,12 @@ static void read_credential(void)
 		*v++ = '\0';
 
 		if (!strcmp(buf, "protocol"))
-			protocol = xstrdup(v);
+			protocol = utf8_to_utf16_dup(v);
 		else if (!strcmp(buf, "host"))
-			host = xstrdup(v);
+			host = utf8_to_utf16_dup(v);
 		else if (!strcmp(buf, "path"))
-			path = xstrdup(v);
+			path = utf8_to_utf16_dup(v);
 		else if (!strcmp(buf, "username")) {
-			username = xstrdup(v);
 			wusername = utf8_to_utf16_dup(v);
 		} else if (!strcmp(buf, "password"))
 			password = utf8_to_utf16_dup(v);
@@ -333,22 +276,20 @@ int main(int argc, char *argv[])
 		return 0;
 
 	/* prepare 'target', the unique key for the credential */
-	strncat(target_buf, "git:", sizeof(target_buf));
-	strncat(target_buf, protocol, sizeof(target_buf));
-	strncat(target_buf, "://", sizeof(target_buf));
-	if (username) {
-		strncat(target_buf, username, sizeof(target_buf));
-		strncat(target_buf, "@", sizeof(target_buf));
+	wcscpy(target, L"git:");
+	wcsncat(target, protocol, ARRAY_SIZE(target));
+	wcsncat(target, L"://", ARRAY_SIZE(target));
+	if (wusername) {
+		wcsncat(target, wusername, ARRAY_SIZE(target));
+		wcsncat(target, L"@", ARRAY_SIZE(target));
 	}
 	if (host)
-		strncat(target_buf, host, sizeof(target_buf));
+		wcsncat(target, host, ARRAY_SIZE(target));
 	if (path) {
-		strncat(target_buf, "/", sizeof(target_buf));
-		strncat(target_buf, path, sizeof(target_buf));
+		wcsncat(target, L"/", ARRAY_SIZE(target));
+		wcsncat(target, path, ARRAY_SIZE(target));
 	}
 
-	target = utf8_to_utf16_dup(target_buf);
-
 	if (!strcmp(argv[1], "get"))
 		get_credential();
 	else if (!strcmp(argv[1], "store"))
-- 
1.8.0.msysgit.0.4.g4e40dea

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