Re: [PATCH] credential/wincred: store oauth_refresh_token

From: M Hickford <redacted>

a5c7656 (credential: new attribute oauth_refresh_token) introduced
a new confidential credential attribute for helpers to store.

We encode the new attribute in the CredentialBlob, separated by
newline:

    hunter2
    oauth_refresh_token=xyzzy

This is extensible and backwards compatible. The credential protocol
already assumes that attribute values do not contain newlines.

Alternatives considered: store oauth_refresh_token in a wincred
attribute. This would be insecure because wincred assumes attribute
values to be non-confidential.

Signed-off-by: M Hickford <redacted>
---
    credential/wincred: store oauth_refresh_token

    I'm not confident in C and found string manipulation difficult, so
    please review carefully.

    I tested on Linux, cross compiling with Zig make CC="zig cc -target
    x86_64-windows-gnu" and tested make GIT_TEST_CREDENTIAL_HELPER=wincred
    t0303-credential-external.sh (with a shell script git-credential-wincred
    that wraps wine64 git-credential-wincred.exe "$@")

    See also similar patch for credential-libsecret "[PATCH v4]
    credential/libsecret: store new attributes"
    https://lore.kernel.org/git/pull.1469.v4.git.git.1684306540947.gitgitgadget@gmail.com/T/#u (local)

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1534%2Fhickford%2Fwincred-refresh-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1534/hickford/wincred-refresh-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1534

 .../wincred/git-credential-wincred.c          | 40 ++++++++++++++++---
 t/t0303-credential-external.sh                |  1 +
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/contrib/credential/wincred/git-credential-wincred.c b/contrib/credential/wincred/git-credential-wincred.c
index 96f10613aee..dc34283b85e 100644
--- a/contrib/credential/wincred/git-credential-wincred.c
+++ b/contrib/credential/wincred/git-credential-wincred.c

@@ -35,7 +35,7 @@ static void *xmalloc(size_t size)
 }

 static WCHAR *wusername, *password, *protocol, *host, *path, target[1024],
-       *password_expiry_utc;
+       *password_expiry_utc, *oauth_refresh_token;

 static void write_item(const char *what, LPCWSTR wbuf, int wlen)
 {

@@ -128,6 +128,11 @@ static void get_credential(void)
        DWORD num_creds;
        int i;
        CREDENTIAL_ATTRIBUTEW *attr;
+       WCHAR *secret;
+       WCHAR *line;
+       WCHAR *remaining_lines;
+       WCHAR *part;
+       WCHAR *remaining_parts;

        if (!CredEnumerateW(L"git:*", 0, &num_creds, &creds))
                return;

@@ -137,9 +142,17 @@ static void get_credential(void)
                if (match_cred(creds[i])) {
                        write_item("username", creds[i]->UserName,
                                creds[i]->UserName ? wcslen(creds[i]->UserName) : 0);
-                       write_item("password",
-                               (LPCWSTR)creds[i]->CredentialBlob,
-                               creds[i]->CredentialBlobSize / sizeof(WCHAR));
+                       secret = xmalloc(creds[i]->CredentialBlobSize);
+                       wcsncpy_s(secret, creds[i]->CredentialBlobSize, (LPCWSTR)creds[i]->CredentialBlob, creds[i]->CredentialBlobSize / sizeof(WCHAR));
+                       line = wcstok_s(secret, L"\r\n", &remaining_lines);
+                       write_item("password", line, wcslen(line));
+                       while(line != NULL) {
+                               part = wcstok_s(line, L"=", &remaining_parts);
+                               if (!wcscmp(part, L"oauth_refresh_token")) {
+                                       write_item("oauth_refresh_token", remaining_parts, wcslen(remaining_parts));
+                               }
+                               line = wcstok_s(NULL, L"\r\n", &remaining_lines);
+                       }
                        for (int j = 0; j < creds[i]->AttributeCount; j++) {
                                attr = creds[i]->Attributes + j;
                                if (!wcscmp(attr->Keyword, L"git_password_expiry_utc")) {

@@ -148,6 +161,7 @@ static void get_credential(void)
                                        break;
                                }
                        }
+                       free(secret);
                        break;
                }

@@ -158,16 +172,26 @@ static void store_credential(void)
 {
        CREDENTIALW cred;
        CREDENTIAL_ATTRIBUTEW expiry_attr;
+       WCHAR *secret;
+       int wlen;

        if (!wusername || !password)
                return;

+       if (oauth_refresh_token) {
+               wlen = _scwprintf(L"%s\r\noauth_refresh_token=%s", password, oauth_refresh_token);
+               secret = xmalloc(sizeof(WCHAR) * wlen);
+               _snwprintf_s(secret, sizeof(WCHAR) * wlen, wlen, L"%s\r\noauth_refresh_token=%s", password, oauth_refresh_token);
+       } else {
+               secret = _wcsdup(password);
+       }
+
        cred.Flags = 0;
        cred.Type = CRED_TYPE_GENERIC;
        cred.TargetName = target;
        cred.Comment = L"saved by git-credential-wincred";
-       cred.CredentialBlobSize = (wcslen(password)) * sizeof(WCHAR);
-       cred.CredentialBlob = (LPVOID)password;
+       cred.CredentialBlobSize = wcslen(secret) * sizeof(WCHAR);
+       cred.CredentialBlob = (LPVOID)_wcsdup(secret);
        cred.Persist = CRED_PERSIST_LOCAL_MACHINE;
        cred.AttributeCount = 0;
        cred.Attributes = NULL;

@@ -182,6 +206,8 @@ static void store_credential(void)
        cred.TargetAlias = NULL;
        cred.UserName = wusername;

+       free(secret);
+
        if (!CredWriteW(&cred, 0))
                die("CredWrite failed");
 }

@@ -253,6 +279,8 @@ static void read_credential(void)
                        password = utf8_to_utf16_dup(v);
                else if (!strcmp(buf, "password_expiry_utc"))
                        password_expiry_utc = utf8_to_utf16_dup(v);
+               else if (!strcmp(buf, "oauth_refresh_token"))
+                       oauth_refresh_token = utf8_to_utf16_dup(v);
                /*
                 * Ignore other lines; we don't know what they mean, but
                 * this future-proofs us when later versions of git do

diff --git a/t/t0303-credential-external.sh b/t/t0303-credential-external.sh
index f028fd14182..51886b8e259 100755
--- a/t/t0303-credential-external.sh
+++ b/t/t0303-credential-external.sh

@@ -45,6 +45,7 @@ test -z "$GIT_TEST_CREDENTIAL_HELPER_SETUP" ||
 helper_test_clean "$GIT_TEST_CREDENTIAL_HELPER"

 helper_test "$GIT_TEST_CREDENTIAL_HELPER"
+helper_test_oauth_refresh_token "$GIT_TEST_CREDENTIAL_HELPER"

 if test -z "$GIT_TEST_CREDENTIAL_HELPER_TIMEOUT"; then
        say "# skipping timeout tests (GIT_TEST_CREDENTIAL_HELPER_TIMEOUT not set)"

base-commit: 9e49351c3060e1fa6e0d2de64505b7becf157f28
--
gitgitgadget