[ovs-dev] [PATCH]lib/stream-windows.c: Grant Access Privilege of Named Pipe to Creator

Ning Wu nwu at vmware.com
Thu Jan 23 07:00:55 UTC 2020


Hi Alin and Anand,

I've rebased the patch and also added some description on the documentation. 
Please help to review.
Thanks.

-----Original Message-----
From: Ning Wu 
Sent: Wednesday, January 22, 2020 16:19
To: Alin Serdean <aserdean at cloudbasesolutions.com>; dev at openvswitch.org; Anand Kumar <kumaranand at vmware.com>
Cc: Lina Li <linali at vmware.com>; Roy Luo <luoroy at vmware.com>
Subject: [PATCH]lib/stream-windows.c: Grant Access Privilege of Named Pipe to Creator

>From e42950665acee9aab941b26ebdd067ca0de908a3 Mon Sep 17 00:00:00 2001
From: Ning Wu <nwu at vmware.com>
Date: Tue, 21 Jan 2020 23:46:58 -0800
Subject: [PATCH]lib/stream-windows.c: Grant Access Privilege of Named Pipe to Creator

Current implementation of ovs on windows only allows LocalSystem and Administrators to access the named pipe created with API of ovs.
Thus any service that needs to invoke the API to create named pipe has to run as System account to interactive with ovs. It causes the system more vulnerable if one of those services was break into.
The patch adds the creator owner account to allowed ACLs.

Signed-off-by: Ning Wu <nwu at vmware.com>
---
 Documentation/ref/ovsdb.7.rst |  3 ++-
 lib/stream-windows.c          | 33 ++++++++++++++++++++++++++++++++-
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/Documentation/ref/ovsdb.7.rst b/Documentation/ref/ovsdb.7.rst index b1f3f5d..da4dbed 100644
--- a/Documentation/ref/ovsdb.7.rst
+++ b/Documentation/ref/ovsdb.7.rst
@@ -422,7 +422,8 @@ punix:<file>
     named <file>.
 
     On Windows, listens on a local named pipe, creating a named pipe
-    <file> to mimic the behavior of a Unix domain socket.
+    <file> to mimic the behavior of a Unix domain socket. The ACLs of the named
+    pipe include LocalSystem, Administrators, and Creator Owner.
 
 All IP-based connection methods accept IPv4 and IPv6 addresses.  To specify an
 IPv6 address, wrap it in square brackets, e.g.  ``ssl:[::1]:6640``.  Passive diff --git a/lib/stream-windows.c b/lib/stream-windows.c index 34bc610..5c4c55e 100644
--- a/lib/stream-windows.c
+++ b/lib/stream-windows.c
@@ -41,7 +41,7 @@ static void maybe_unlink_and_free(char *path);  #define LOCAL_PREFIX "\\\\.\\pipe\\"
 
 /* Size of the allowed PSIDs for securing Named Pipe. */ -#define ALLOWED_PSIDS_SIZE 2
+#define ALLOWED_PSIDS_SIZE 3
 
 /* This function has the purpose to remove all the slashes received in s. */  static char * @@ -412,6 +412,9 @@ create_pnpipe(char *name)
     PACL acl = NULL;
     PSECURITY_DESCRIPTOR psd = NULL;
     HANDLE npipe;
+    HANDLE hToken = NULL;
+    DWORD dwBufSize = 0;
+    PTOKEN_USER pTokenUsr = NULL;
 
     /* Disable access over network. */
     if (!AllocateAndInitializeSid(&sia, 1, SECURITY_NETWORK_RID, @@ -438,6 +441,32 @@ create_pnpipe(char *name)
         goto handle_error;
     }
 
+    /* Open the access token of calling process */
+    if (!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &hToken)) {
+        VLOG_ERR_RL(&rl, "Error opening access token of calling process.");
+        goto handle_error;
+    }
+
+    /* get the buffer size buffer needed for SID */
+    GetTokenInformation(hToken, TokenUser, NULL, 0, &dwBufSize);
+
+    pTokenUsr = xmalloc(dwBufSize);
+    memset(pTokenUsr, 0, dwBufSize);
+
+    /* Retrieve the token information in a TOKEN_USER structure. */
+    if (!GetTokenInformation(hToken, TokenUser, pTokenUsr, dwBufSize,
+        &dwBufSize)) {
+        VLOG_ERR_RL(&rl, "Error retrieving token information.");
+        goto handle_error;
+    }
+    CloseHandle(hToken);
+
+    if (!IsValidSid(pTokenUsr->User.Sid)) {
+        VLOG_ERR_RL(&rl, "Invalid SID.");
+        goto handle_error;
+    }
+    allowedPsid[2] = pTokenUsr->User.Sid;
+
     for (int i = 0; i < ALLOWED_PSIDS_SIZE; i++) {
         aclSize += sizeof(ACCESS_ALLOWED_ACE) +
                    GetLengthSid(allowedPsid[i]) - @@ -490,11 +519,13 @@ create_pnpipe(char *name)
     npipe = CreateNamedPipe(name, PIPE_ACCESS_DUPLEX | FILE_FLAG_OVERLAPPED,
                             PIPE_TYPE_MESSAGE | PIPE_READMODE_BYTE | PIPE_WAIT,
                             64, BUFSIZE, BUFSIZE, 0, &sa);
+    free(pTokenUsr);
     free(acl);
     free(psd);
     return npipe;
 
 handle_error:
+    free(pTokenUsr);
     free(acl);
     free(psd);
     return INVALID_HANDLE_VALUE;
--
2.6.2

-----Original Message-----
From: Alin Serdean <aserdean at cloudbasesolutions.com>
Sent: Wednesday, January 22, 2020 12:19
To: Ning Wu <nwu at vmware.com>; dev at openvswitch.org; Anand Kumar <kumaranand at vmware.com>
Cc: Lina Li <linali at vmware.com>; Roy Luo <luoroy at vmware.com>
Subject: RE: [PATCH] Grant Access Privilege of Named Pipe to Creator

Hi,

Sorry I missed the email.

The direction sounds ok with me. It will surely help with unit tests, since right now they require elevated permissions.

Adding also Anand in the loop.
Anand do you like the idea?

Please also add a few lines to the documentation so users are aware of the change.

The patch as is, fails to apply. Rebase on master.

Also please change the title so it is in compliance with:
https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdocs.openvswitch.org%2Fen%2Flatest%2Finternals%2Fcontributing%2Fsubmitting-patches%2F%23email-subject&data=02%7C01%7Cnwu%40vmware.com%7Cf87a8fa19a3d438325d008d79ef2400c%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C1%7C637152635616314521&sdata=h73zweLknUd2m9ReaYEe94QNR4wj3q5TilBV8tQmjiw%3D&reserved=0 

Thanks,
Alin.

> -----Original Message-----
> From: Ning Wu <nwu at vmware.com>
> Sent: Monday, January 20, 2020 4:16 AM
> To: dev at openvswitch.org; Alin Serdean 
> <aserdean at cloudbasesolutions.com>
> Cc: Lina Li <linali at vmware.com>; Roy Luo <luoroy at vmware.com>
> Subject: RE: [PATCH] Grant Access Privilege of Named Pipe to Creator
> 
> Hi Alin,
> 
> 
> 
> Could you please help to give some comment?
> 
> Thanks.
> 
> 
> 
> From: Ning Wu
> Sent: Friday, January 17, 2020 15:15
> To: dev at openvswitch.org; Alin Serdean 
> <aserdean at cloudbasesolutions.com>
> Cc: Lina Li <linali at vmware.com>; Roy Luo <luoroy at vmware.com>
> Subject: [PATCH] Grant Access Privilege of Named Pipe to Creator
> 
> 
> 
> Current implementation of ovs on windows only allows LocalSystem and
> 
> Administrators to access the named pipe created with API of ovs.
> 
> Thus any service that needs to invoke the API to create named pipe
> 
> has to run as System account to interactive with ovs. It causes the
> 
> system more vulnerable if one of those services was break into.
> 
> The patch adds the creator owner account to allowed ACLs.
> 
> 
> 
> Signed-off-by: Ning Wu <nwu at vmware.com <mailto:nwu at vmware.com> >
> 
> ---
> 
> lib/stream-windows.c | 33 ++++++++++++++++++++++++++++++++-
> 
> 1 file changed, 32 insertions(+), 1 deletion(-)
> 
> 
> 
> diff --git a/lib/stream-windows.c b/lib/stream-windows.c
> 
> index 34bc610..0cad927 100644
> 
> --- a/lib/stream-windows.c
> 
> +++ b/lib/stream-windows.c
> 
> @@ -41,7 +41,7 @@ static void maybe_unlink_and_free(char *path);
> 
> #define LOCAL_PREFIX "\\\\.\\pipe\\ <file://.//pipe/> "
> 
> 
> 
> /* Size of the allowed PSIDs for securing Named Pipe. */
> 
> -#define ALLOWED_PSIDS_SIZE 2
> 
> +#define ALLOWED_PSIDS_SIZE 3
> 
> 
> 
> /* This function has the purpose to remove all the slashes received in 
> s. */
> 
> static char *
> 
> @@ -412,6 +412,9 @@ create_pnpipe(char *name)
> 
>      PACL acl = NULL;
> 
>      PSECURITY_DESCRIPTOR psd = NULL;
> 
>      HANDLE npipe;
> 
> +    HANDLE hToken = NULL;
> 
> +    DWORD dwBufSize = 0;
> 
> +    PTOKEN_USER pTokenUsr = NULL;
> 
> 
> 
>      /* Disable access over network. */
> 
>      if (!AllocateAndInitializeSid(&sia, 1, SECURITY_NETWORK_RID,
> 
> @@ -438,6 +441,32 @@ create_pnpipe(char *name)
> 
>          goto handle_error;
> 
>      }
> 
> 
> 
> +    /* Open the access token of calling process */
> 
> +    if (!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &hToken)) 
> + {
> 
> +       VLOG_ERR_RL(&rl, "Error opening access token of calling 
> + process.");
> 
> +        goto handle_error;
> 
> +    }
> 
> +
> 
> +    /* get the buffer size buffer needed for SID */
> 
> +    GetTokenInformation(hToken, TokenUser, NULL, 0, &dwBufSize);
> 
> +
> 
> +    pTokenUsr = xmalloc(dwBufSize);
> 
> +    memset(pTokenUsr, 0, dwBufSize);
> 
> +
> 
> +    /* Retrieve the token information in a TOKEN_USER structure. */
> 
> +    if (!GetTokenInformation(hToken, TokenUser, pTokenUsr, dwBufSize,
> 
> +        &dwBufSize)) {
> 
> +        VLOG_ERR_RL(&rl, "Error retrieving token information.");
> 
> +        goto handle_error;
> 
> +    }
> 
> +    CloseHandle(hToken);
> 
> +
> 
> +    if (!IsValidSid(pTokenUsr->User.Sid)) {
> 
> +        VLOG_ERR_RL(&rl, "Invalid SID.");
> 
> +        goto handle_error;
> 
> +    }
> 
> +    allowedPsid[2] = pTokenUsr->User.Sid;
> 
> +
> 
>      for (int i = 0; i < ALLOWED_PSIDS_SIZE; i++) {
> 
>          aclSize += sizeof(ACCESS_ALLOWED_ACE) +
> 
>                     GetLengthSid(allowedPsid[i]) -
> 
> @@ -490,11 +519,13 @@ create_pnpipe(char *name)
> 
>      npipe = CreateNamedPipe(name, PIPE_ACCESS_DUPLEX | 
> FILE_FLAG_OVERLAPPED,
> 
>                              PIPE_TYPE_MESSAGE | PIPE_READMODE_BYTE | 
> PIPE_WAIT,
> 
>                              64, BUFSIZE, BUFSIZE, 0, &sa);
> 
> +    free(pTokenUsr);
> 
>      free(acl);
> 
>      free(psd);
> 
>      return npipe;
> 
> 
> 
> handle_error:
> 
> +    free(pTokenUsr);
> 
>      free(acl);
> 
>      free(psd);
> 
>      return INVALID_HANDLE_VALUE;
> 
> --
> 
> 2.6.2
> 
> 



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