Re: [PATCH] wincred: improve compatibility with windows versions
From: Erik Faye-Lund <hidden>
Date: 2016-06-15 22:55:39
On Fri, Jan 4, 2013 at 9:28 PM, Karsten Blees [off-list ref] wrote:
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. While we're at it, optionally accept CRLF (instead of LF only) to simplify debugging in bash / cmd. Signed-off-by: Karsten Blees <redacted> --- Hi, I tried the windows credential helper yesterday and found that it doesn't work on XP at all, and doesn't work properly in combination with Win7 credential manager tools. So here's a patch that reduces it to the functionality provided / expected by Windows. @Erik, Jeff: Please let me know if I'm missing something and the use of Cred[Un]PackAuthenticationBuffer or CREDENTIAL_ATTRIBUTEs actually served a useful purpose.
The only reason why I used Cred[Un]PackAuthenticationBuffer, were that I wasn't aware that it was possible any other way. I didn't even know there was a Windows Credential Manager in Windows XP. The credential attributes were because they were convenient, and I'm not sure I understand what you mean about the Win7 credential manager tools. I did test my code with it - in fact, it was a very useful tool for debugging the helper. Are you referring to the credentials not *looking* like normal HTTP-credentials? If so, I simply didn't see that as a goal. Why would it be? Compatibility with IE? We already lose that with our "git:" prefix in the target, no? Perhaps we can lose the "git:"-prefix, and gain IE-compatibility when the protocol matches? But, if we do any of these changes, does this mean I will lose my existing credentials? It's probably not a big deal, but it's worth a mention, isn't it?
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@@ -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;
Perhaps get rid of credui also?
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static CredWriteWT CredWriteW; -static CredUnPackAuthenticationBufferWT CredUnPackAuthenticationBufferW; static CredEnumerateWT CredEnumerateW; -static CredPackAuthenticationBufferWT CredPackAuthenticationBufferW; static CredFreeT CredFree; static CredDeleteWT CredDeleteW;@@ -88,74 +76,64 @@ static void load_cred_funcs(void) { /* load DLLs */ advapi = LoadLibrary("advapi32.dll"); - credui = LoadLibrary("credui.dll"); - if (!advapi || !credui) + if (!advapi) die("failed to load DLLs");
It's not multiple DLLs any more, so perhaps "failed to load advapi32.dll" instead?
-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);
}When the password-blob is simply UTF-16 encoded, are the zero-termination not included? That's the reason for this change, right?
-static int match_attr(const CREDENTIALW *cred, const WCHAR *keyword,
- const char *want)
+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 start = *ptarget;
+ LPCWSTR end = *delim ? wcsstr(start, delim) : start + wcslen(start);
+ int len = end ? end - start : wcslen(start);
+ /* update ptarget if we either found a delimiter or need a match */
+ if (end || want)
+ *ptarget = end ? end + wcslen(delim) : start + len;
+ return !want || (!wcsncmp(want, start, len) && !want[len]);
}I'm a bit tired now, but I'm having a hard time reading this code. Right now it seems it's a bit too ternary-expression heavy for my taste, though.
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"");
}Ugh, it feels a bit wrong to store and verify the username twice. Do we really have to? The target needs to be unique, even if two different usernames are stored for the same site under the same conditions. So probably. It just doesn't feel quite right.
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@@ -165,44 +143,15 @@ 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); -}
Nice!
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- -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)@@ -215,40 +164,18 @@ static void store_credential(void) 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"); }
Nice.
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@@ -284,10 +211,13 @@ static void read_credential(void) while (fgets(buf, sizeof(buf), stdin)) { char *v; + int len = strlen(buf); + /* strip trailing CR / LF */ + while (len && strchr("\r\n", buf[len - 1])) + buf[--len] = 0; - if (!strcmp(buf, "\n")) + if (!*buf) break; - buf[strlen(buf)-1] = '\0'; v = strchr(buf, '='); if (!v)
I think this part deserves a separate patch, no?
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@@ -295,13 +225,12 @@ 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);
So, you need the strings as UTF-16 instead so you can match against them...
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@@ -330,22 +259,20 @@ 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); -
...Which means that you are composing a UTF-16 target directly rather than ASCII. Looks sane. -- *** Please reply-to-all at all times *** *** (do not pretend to know who is subscribed and who is not) *** *** Please avoid top-posting. *** The msysGit Wiki is here: https://github.com/msysgit/msysgit/wiki - Github accounts are free. You received this message because you are subscribed to the Google Groups "msysGit" group. To post to this group, send email to msysgit@googlegroups.com To unsubscribe from this group, send email to msysgit+unsubscribe@googlegroups.com For more options, and view previous threads, visit this group at http://groups.google.com/group/msysgit?hl=en_US?hl=en