[PATCH] cifs: set client time as MsvAvTimestamp from CHALLENGE

Discussion:

[PATCH] cifs: set client time as MsvAvTimestamp from CHALLENGE_MESSAGE.TargetInfo

Namjae Jeon

2014-08-25 05:29:44 UTC

Windows machine has extended security feature which refuse to allow
authentication when there is time difference between server time and
client time when ntlmv2 negotiation is used. This problem is prevalent
in embedded enviornment where system time is set to default 1970.

Modern servers send the server timestamp in the TargetInfo Av_Pair
structure in the challenge message [see MS-NLMP 2.2.2.1]
In [MS-NLMP 3.1.5.1.2] it is explicitly mentioned that the client must
use the server provided timestamp if present OR current time if it is
not.

Cc: Simo <simo-***@public.gmane.org>
Signed-off-by: Namjae Jeon <namjae.jeon-***@public.gmane.org>
Signed-off-by: Ashish Sangwan <a.sangwan-***@public.gmane.org>
---
fs/cifs/cifsencrypt.c | 6 ++++--
fs/cifs/cifsglob.h | 2 ++
fs/cifs/sess.c | 21 +++++++++++++++++++++
3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c
index 4934347..3ec44f8 100644
--- a/fs/cifs/cifsencrypt.c
+++ b/fs/cifs/cifsencrypt.c
@@ -671,8 +671,10 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
(ses->auth_key.response + CIFS_SESS_KEY_SIZE);
ntlmv2->blob_signature = cpu_to_le32(0x00000101);
ntlmv2->reserved = 0;
- /* Must be within 5 minutes of the server */
- ntlmv2->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
+ if (ses->serverTime)
+ ntlmv2->time = ses->serverTime;
+ else
+ ntlmv2->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
get_random_bytes(&ntlmv2->client_chal, sizeof(ntlmv2->client_chal));
ntlmv2->reserved2 = 0;

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index ce24c1f..1102822 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -796,6 +796,8 @@ struct cifs_ses {
enum securityEnum sectype; /* what security flavor was specified? */
bool sign; /* is signing required? */
bool need_reconnect:1; /* connection reset, uid now invalid */
+ __u64 serverTime; /* Keeps a track of server time sent by server
+ during NTLM challenge in little endian */
#ifdef CONFIG_CIFS_SMB2
__u16 session_flags;
char smb3signingkey[SMB3_SIGN_KEY_SIZE]; /* for signing smb3 packets */
diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index 07fe97a..0762377 100644
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -277,6 +277,26 @@ static void decode_ascii_ssetup(char **pbcc_area, __u16 bleft,
cifs_dbg(FYI, "ascii: bytes left %d\n", bleft);
}

+static void
+get_ntlmv2_server_time(struct cifs_ses *ses)
+{
+#define MsvAvEOL 0x0000
+#define MsvAvTimestamp 0x0007
+ char *payload = ses->auth_key.response;
+ u16 AvId, AvLen;
+
+ do {
+ AvId = le16_to_cpu(*payload);
+ AvLen = le16_to_cpu(*(payload + sizeof(u16)));
+ payload += AvLen + (2 * sizeof(u16));
+ } while (AvId != MsvAvTimestamp && AvId != MsvAvEOL);
+
+ if (AvId == MsvAvTimestamp)
+ memcpy(&(ses->serverTime), (payload - AvLen), sizeof(__u64));
+ else
+ ses->serverTime = 0;
+}
+
int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
struct cifs_ses *ses)
{
@@ -322,6 +342,7 @@ int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
return -ENOMEM;
}
ses->auth_key.len = tilen;
+ get_ntlmv2_server_time(ses);
}

return 0;

--
1.7.7

Simo

2014-08-25 13:12:39 UTC

Permalink

Post by Namjae Jeon
Windows machine has extended security feature which refuse to allow
authentication when there is time difference between server time and
client time when ntlmv2 negotiation is used. This problem is prevalent
in embedded enviornment where system time is set to default 1970.
Modern servers send the server timestamp in the TargetInfo Av_Pair
structure in the challenge message [see MS-NLMP 2.2.2.1]
In [MS-NLMP 3.1.5.1.2] it is explicitly mentioned that the client must
use the server provided timestamp if present OR current time if it is
not.
---
fs/cifs/cifsencrypt.c | 6 ++++--
fs/cifs/cifsglob.h | 2 ++
fs/cifs/sess.c | 21 +++++++++++++++++++++
3 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c
index 4934347..3ec44f8 100644
--- a/fs/cifs/cifsencrypt.c
+++ b/fs/cifs/cifsencrypt.c
@@ -671,8 +671,10 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
(ses->auth_key.response + CIFS_SESS_KEY_SIZE);
ntlmv2->blob_signature = cpu_to_le32(0x00000101);
ntlmv2->reserved = 0;
- /* Must be within 5 minutes of the server */
- ntlmv2->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
+ if (ses->serverTime)
+ ntlmv2->time = ses->serverTime;
+ else
+ ntlmv2->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
get_random_bytes(&ntlmv2->client_chal, sizeof(ntlmv2->client_chal));
ntlmv2->reserved2 = 0;
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index ce24c1f..1102822 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -796,6 +796,8 @@ struct cifs_ses {
enum securityEnum sectype; /* what security flavor was specified? */
bool sign; /* is signing required? */
bool need_reconnect:1; /* connection reset, uid now invalid */
+ __u64 serverTime; /* Keeps a track of server time sent by server
+ during NTLM challenge in little endian */
#ifdef CONFIG_CIFS_SMB2
__u16 session_flags;
char smb3signingkey[SMB3_SIGN_KEY_SIZE]; /* for signing smb3 packets */
diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index 07fe97a..0762377 100644
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -277,6 +277,26 @@ static void decode_ascii_ssetup(char **pbcc_area, __u16 bleft,
cifs_dbg(FYI, "ascii: bytes left %d\n", bleft);
}
+static void
+get_ntlmv2_server_time(struct cifs_ses *ses)
+{
+#define MsvAvEOL 0x0000
+#define MsvAvTimestamp 0x0007
+ char *payload = ses->auth_key.response;
+ u16 AvId, AvLen;
+
+ do {
+ AvId = le16_to_cpu(*payload);
+ AvLen = le16_to_cpu(*(payload + sizeof(u16)));
+ payload += AvLen + (2 * sizeof(u16));
+ } while (AvId != MsvAvTimestamp && AvId != MsvAvEOL);
+
+ if (AvId == MsvAvTimestamp)
+ memcpy(&(ses->serverTime), (payload - AvLen), sizeof(__u64));
+ else
+ ses->serverTime = 0;
+}
+
int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
struct cifs_ses *ses)
{
@@ -322,6 +342,7 @@ int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
return -ENOMEM;
}
ses->auth_key.len = tilen;
+ get_ntlmv2_server_time(ses);
}
return 0;

I'll let a cifs maintainer ack or nack the implementation, but from a
logic pov it looks good.

Simo.

Namjae Jeon

2014-08-26 00:19:32 UTC

Permalink

Post by Simo

Post by Namjae Jeon
+
int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
struct cifs_ses *ses)
{
@@ -322,6 +342,7 @@ int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
return -ENOMEM;
}
ses->auth_key.len = tilen;
+ get_ntlmv2_server_time(ses);
}
return 0;

I'll let a cifs maintainer ack or nack the implementation, but from a
logic pov it looks good.

Thanks for your review!

Post by Simo
Simo.

Shirish Pargaonkar

2014-08-25 15:12:42 UTC

Permalink

This patch looks correct but we have these defines in ntlmssp.h.

Post by Namjae Jeon
+ char *payload = ses->auth_key.response;
+ u16 AvId, AvLen;
+
+ do {
+ AvId = le16_to_cpu(*payload);
+ AvLen = le16_to_cpu(*(payload + sizeof(u16)));
+ payload += AvLen + (2 * sizeof(u16));
+ } while (AvId != MsvAvTimestamp && AvId != MsvAvEOL);
+
+ if (AvId == MsvAvTimestamp)
+ memcpy(&(ses->serverTime), (payload - AvLen), sizeof(__u64));
+ else
+ ses->serverTime = 0;
+}
+
int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
struct cifs_ses *ses)
{
@@ -322,6 +342,7 @@ int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
return -ENOMEM;
}
ses->auth_key.len = tilen;
+ get_ntlmv2_server_time(ses);
}
return 0;
--
1.7.7
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Namjae Jeon

2014-08-26 00:20:44 UTC

Permalink

Post by Shirish Pargaonkar

This patch looks correct but we have these defines in ntlmssp.h.

Okay, I will send v2 patch.
Thanks for your reivew!

Steve French

2014-08-26 00:28:52 UTC

Permalink

Would be helpful as well to note in the patch description whether this
was observed so far only to Windows servers (or whether it affects
mounts to Samba as well e.g.)

Post by Namjae Jeon

Post by Shirish Pargaonkar

This patch looks correct but we have these defines in ntlmssp.h.

Okay, I will send v2 patch.
Thanks for your reivew!

--
Thanks,

Steve

Namjae Jeon

2014-08-26 00:34:52 UTC

Permalink

Post by Steve French
Would be helpful as well to note in the patch description whether this
was observed so far only to Windows servers (or whether it affects
mounts to Samba as well e.g.)

Okay, I will update patch description also. :)

Thanks.

Post by Steve French

Post by Namjae Jeon

Post by Shirish Pargaonkar

This patch looks correct but we have these defines in ntlmssp.h.

Okay, I will send v2 patch.
Thanks for your reivew!

--
Thanks,
Steve