From: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
Set an ACL on the named pipe to allow the well-known group EVERYONE
to read and write to the IPC server's named pipe. In the event that
the daemon was started with elevation, allow non-elevated clients
to communicate with the daemon.
Signed-off-by: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
---
compat/simple-ipc/ipc-win32.c | 140 +++++++++++++++++++++++++++++++---
1 file changed, 129 insertions(+), 11 deletions(-)
diff --git a/compat/simple-ipc/ipc-win32.c b/compat/simple-ipc/ipc-win32.c
index 6c8a308de13..374ae2f81c7 100644
--- a/compat/simple-ipc/ipc-win32.c
+++ b/compat/simple-ipc/ipc-win32.c
@@ -3,6 +3,8 @@
#include "strbuf.h"
#include "pkt-line.h"
#include "thread-utils.h"
+#include "accctrl.h"
+#include "aclapi.h"
#ifndef SUPPORTS_SIMPLE_IPC
/*
@@ -591,11 +593,132 @@ finished:
return NULL;
}
+/*
+ * We need to build a Windows "SECURITY_ATTRIBUTES" object and use it
+ * to apply an ACL when we create the initial instance of the Named
+ * Pipe. The construction is somewhat involved and consists of
+ * several sequential steps and intermediate objects.
+ *
+ * We use this structure to hold these intermediate pointers so that
+ * we can free them as a group. (It is unclear from the docs whether
+ * some of these intermediate pointers can be freed before we are
+ * finished using the "lpSA" member.)
+ */
+struct my_sa_data
+{
+ PSID pEveryoneSID;
+ PACL pACL;
+ PSECURITY_DESCRIPTOR pSD;
+ LPSECURITY_ATTRIBUTES lpSA;
+};
+
+static void init_sa(struct my_sa_data *d)
+{
+ memset(d, 0, sizeof(*d));
+}
+
+static void release_sa(struct my_sa_data *d)
+{
+ if (d->pEveryoneSID)
+ FreeSid(d->pEveryoneSID);
+ if (d->pACL)
+ LocalFree(d->pACL);
+ if (d->pSD)
+ LocalFree(d->pSD);
+ if (d->lpSA)
+ LocalFree(d->lpSA);
+
+ memset(d, 0, sizeof(*d));
+}
+
+/*
+ * Create SECURITY_ATTRIBUTES to apply to the initial named pipe. The
+ * creator of the first server instance gets to set the ACLs on it.
+ *
+ * We allow the well-known group `EVERYONE` to have read+write access
+ * to the named pipe so that clients can send queries to the daemon
+ * and receive the response.
+ *
+ * Normally, this is not necessary since the daemon is usually
+ * automatically started by a foreground command like `git status`,
+ * but in those cases where an elevated Git command started the daemon
+ * (such that the daemon itself runs with elevation), we need to add
+ * the ACL so that non-elevated commands can write to it.
+ *
+ * The following document was helpful:
+ * https://docs.microsoft.com/en-us/windows/win32/secauthz/creating-a-security-descriptor-for-a-new-object-in-c--
+ *
+ * Returns d->lpSA set to a SA or NULL.
+ */
+static LPSECURITY_ATTRIBUTES get_sa(struct my_sa_data *d)
+{
+ SID_IDENTIFIER_AUTHORITY sid_auth_world = SECURITY_WORLD_SID_AUTHORITY;
+#define NR_EA (1)
+ EXPLICIT_ACCESS ea[NR_EA];
+ DWORD dwResult;
+
+ if (!AllocateAndInitializeSid(&sid_auth_world, 1,
+ SECURITY_WORLD_RID, 0,0,0,0,0,0,0,
+ &d->pEveryoneSID)) {
+ DWORD gle = GetLastError();
+ trace2_data_intmax("ipc-debug", NULL, "alloc-world-sid/gle",
+ (intmax_t)gle);
+ goto fail;
+ }
+
+ memset(ea, 0, NR_EA * sizeof(EXPLICIT_ACCESS));
+
+ ea[0].grfAccessPermissions = GENERIC_READ | GENERIC_WRITE;
+ ea[0].grfAccessMode = SET_ACCESS;
+ ea[0].grfInheritance = NO_INHERITANCE;
+ ea[0].Trustee.MultipleTrusteeOperation = NO_MULTIPLE_TRUSTEE;
+ ea[0].Trustee.TrusteeForm = TRUSTEE_IS_SID;
+ ea[0].Trustee.TrusteeType = TRUSTEE_IS_WELL_KNOWN_GROUP;
+ ea[0].Trustee.ptstrName = (LPTSTR)d->pEveryoneSID;
+
+ dwResult = SetEntriesInAcl(NR_EA, ea, NULL, &d->pACL);
+ if (dwResult != ERROR_SUCCESS) {
+ DWORD gle = GetLastError();
+ trace2_data_intmax("ipc-debug", NULL, "set-acl-entry/gle",
+ (intmax_t)gle);
+ trace2_data_intmax("ipc-debug", NULL, "set-acl-entry/dw",
+ (intmax_t)dwResult);
+ goto fail;
+ }
+
+ d->pSD = (PSECURITY_DESCRIPTOR)LocalAlloc(
+ LPTR, SECURITY_DESCRIPTOR_MIN_LENGTH);
+ if (!InitializeSecurityDescriptor(d->pSD, SECURITY_DESCRIPTOR_REVISION)) {
+ DWORD gle = GetLastError();
+ trace2_data_intmax("ipc-debug", NULL, "init-sd/gle", (intmax_t)gle);
+ goto fail;
+ }
+
+ if (!SetSecurityDescriptorDacl(d->pSD, TRUE, d->pACL, FALSE)) {
+ DWORD gle = GetLastError();
+ trace2_data_intmax("ipc-debug", NULL, "set-sd-dacl/gle", (intmax_t)gle);
+ goto fail;
+ }
+
+ d->lpSA = (LPSECURITY_ATTRIBUTES)LocalAlloc(LPTR, sizeof(SECURITY_ATTRIBUTES));
+ d->lpSA->nLength = sizeof(SECURITY_ATTRIBUTES);
+ d->lpSA->lpSecurityDescriptor = d->pSD;
+ d->lpSA->bInheritHandle = FALSE;
+
+ return d->lpSA;
+
+fail:
+ release_sa(d);
+ return NULL;
+}
+
static HANDLE create_new_pipe(wchar_t *wpath, int is_first)
{
HANDLE hPipe;
DWORD dwOpenMode, dwPipeMode;
- LPSECURITY_ATTRIBUTES lpsa = NULL;
+ struct my_sa_data my_sa_data;
+
+ init_sa(&my_sa_data);
dwOpenMode = PIPE_ACCESS_INBOUND | PIPE_ACCESS_OUTBOUND |
FILE_FLAG_OVERLAPPED;
@@ -611,20 +734,15 @@ static HANDLE create_new_pipe(wchar_t *wpath, int is_first)
* set the ACL / Security Attributes on the named
* pipe; subsequent instances inherit and cannot
* change them.
- *
- * TODO Should we allow the application layer to
- * specify security attributes, such as `LocalService`
- * or `LocalSystem`, when we create the named pipe?
- * This question is probably not important when the
- * daemon is started by a foreground user process and
- * only needs to talk to the current user, but may be
- * if the daemon is run via the Control Panel as a
- * System Service.
*/
+ get_sa(&my_sa_data);
}
hPipe = CreateNamedPipeW(wpath, dwOpenMode, dwPipeMode,
- PIPE_UNLIMITED_INSTANCES, 1024, 1024, 0, lpsa);
+ PIPE_UNLIMITED_INSTANCES, 1024, 1024, 0,
+ my_sa_data.lpSA);
+
+ release_sa(&my_sa_data);
return hPipe;
}
--
gitgitgadget
