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simple-ipc/ipc-win32: add Windows ACL to named pipe 

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@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Jeff Hostetler 2021-09-20 15:36:16 +00:00 committed by Junio C Hamano
parent 9bd51d4975
commit 8750249053
1 changed files with 129 additions and 11 deletions
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140
compat/simple-ipc/ipc-win32.c
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@ -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
/*
@ -592,11 +594,132 @@ 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;
@ -612,20 +735,15 @@ 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;
}