Re: [PATCH] credential/wincred: store oauth_refresh_token

>
> Hi. A small patch to git-credential-wincred needs review on the Git
> mailing list https://lore.kernel.org/git/pull.1534.git.1684567247339.gitgitgadget@gmail.com/
> . Does anyone here have the expertise to review?
>
> On Sat, 20 May 2023 at 08:20, M Hickford via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> >
> > From: M Hickford <mirth.hickford@gmail.com>
> >
> > 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 <mirth.hickford@gmail.com>
> > ---
> >     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
> >
> > 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