Re: [PATCH linux-next] cifs: Use data structures to compute NTLMv2response offsets

From: Jeff Layton
Date: Thu Nov 07 2013 - 20:47:51 EST

On Thu, 7 Nov 2013 16:40:57 -0700
Tim Gardner <tim.gardner@xxxxxxxxxxxxx> wrote:

> A bit of cleanup plus some gratuitous variable renaming. I think using
> structures instead of numeric offsets makes this code much more
> understandable.
>
> Also added a comment about current time range expected by
> the server.
>
> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> Cc: Steve French <sfrench@xxxxxxxxx>
> Signed-off-by: Tim Gardner <tim.gardner@xxxxxxxxxxxxx>
> ---
>
> The comment about time of day needing to be within 5 minutes is important (to me
> at least). I spent the best part of a week thinking I had endian issues on powerpc
> when in truth I was just too stupid to notice that the clock
> was not updated. Danged embedded platforms...
>
> checkpatch has some problems with this patch regarding attribute packed, but I chose
> to remain consistent with existing code.
>
> WARNING: __packed is preferred over __attribute__((packed))
> #141: FILE: fs/cifs/cifspdu.h:705:
> + } __attribute__((packed)) challenge;
>
> WARNING: __packed is preferred over __attribute__((packed))
> #142: FILE: fs/cifs/cifspdu.h:706:
> + } __attribute__((packed));
>
> total: 0 errors, 2 warnings, 99 lines checked
>
> Tested on cifs-2.6 for-linus (c481e9feee78c6ce1ba0a1c8c892049f6514f6cf) by mounting
> to iOS 10.8 and Win 8.0 Pro.
>
> rtg
>
> fs/cifs/cifsencrypt.c | 40 ++++++++++++++++++++++++----------------
> fs/cifs/cifspdu.h | 8 +++++++-
> 2 files changed, 31 insertions(+), 17 deletions(-)
>
> diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c
> index fc6f4f3..4934347 100644
> --- a/fs/cifs/cifsencrypt.c
> +++ b/fs/cifs/cifsencrypt.c
> @@ -548,7 +548,13 @@ static int
> CalcNTLMv2_response(const struct cifs_ses *ses, char *ntlmv2_hash)
> {
> int rc;
> - unsigned int offset = CIFS_SESS_KEY_SIZE + 8;
> + struct ntlmv2_resp *ntlmv2 = (struct ntlmv2_resp *)
> + (ses->auth_key.response + CIFS_SESS_KEY_SIZE);
> + unsigned int hash_len;
> +
> + /* The MD5 hash starts at challenge_key.key */
> + hash_len = ses->auth_key.len - (CIFS_SESS_KEY_SIZE +
> + offsetof(struct ntlmv2_resp, challenge.key[0]));
>
> if (!ses->server->secmech.sdeschmacmd5) {
> cifs_dbg(VFS, "%s: can't generate ntlmv2 hash\n", __func__);
> @@ -556,7 +562,7 @@ CalcNTLMv2_response(const struct cifs_ses *ses, char *ntlmv2_hash)
> }
>
> rc = crypto_shash_setkey(ses->server->secmech.hmacmd5,
> - ntlmv2_hash, CIFS_HMAC_MD5_HASH_SIZE);
> + ntlmv2_hash, CIFS_HMAC_MD5_HASH_SIZE);
> if (rc) {
> cifs_dbg(VFS, "%s: Could not set NTLMV2 Hash as a key\n",
> __func__);
> @@ -570,20 +576,21 @@ CalcNTLMv2_response(const struct cifs_ses *ses, char *ntlmv2_hash)
> }
>
> if (ses->server->negflavor == CIFS_NEGFLAVOR_EXTENDED)
> - memcpy(ses->auth_key.response + offset,
> - ses->ntlmssp->cryptkey, CIFS_SERVER_CHALLENGE_SIZE);
> + memcpy(ntlmv2->challenge.key,
> + ses->ntlmssp->cryptkey, CIFS_SERVER_CHALLENGE_SIZE);
> else
> - memcpy(ses->auth_key.response + offset,
> - ses->server->cryptkey, CIFS_SERVER_CHALLENGE_SIZE);
> + memcpy(ntlmv2->challenge.key,
> + ses->server->cryptkey, CIFS_SERVER_CHALLENGE_SIZE);
> rc = crypto_shash_update(&ses->server->secmech.sdeschmacmd5->shash,
> - ses->auth_key.response + offset, ses->auth_key.len - offset);
> + ntlmv2->challenge.key, hash_len);
> if (rc) {
> cifs_dbg(VFS, "%s: Could not update with response\n", __func__);
> return rc;
> }
>
> + /* Note that the MD5 digest over writes anon.challenge_key.key */
> rc = crypto_shash_final(&ses->server->secmech.sdeschmacmd5->shash,
> - ses->auth_key.response + CIFS_SESS_KEY_SIZE);
> + ntlmv2->ntlmv2_hash);
> if (rc)
> cifs_dbg(VFS, "%s: Could not generate md5 hash\n", __func__);
>
> @@ -627,7 +634,7 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
> int rc;
> int baselen;
> unsigned int tilen;
> - struct ntlmv2_resp *buf;
> + struct ntlmv2_resp *ntlmv2;
> char ntlmv2_hash[16];
> unsigned char *tiblob = NULL; /* target info blob */
>
> @@ -660,13 +667,14 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
> }
> ses->auth_key.len += baselen;
>
> - buf = (struct ntlmv2_resp *)
> + ntlmv2 = (struct ntlmv2_resp *)
> (ses->auth_key.response + CIFS_SESS_KEY_SIZE);
> - buf->blob_signature = cpu_to_le32(0x00000101);
> - buf->reserved = 0;
> - buf->time = cpu_to_le64(cifs_UnixTimeToNT(CURRENT_TIME));
> - get_random_bytes(&buf->client_chal, sizeof(buf->client_chal));
> - buf->reserved2 = 0;
> + 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));
> + get_random_bytes(&ntlmv2->client_chal, sizeof(ntlmv2->client_chal));
> + ntlmv2->reserved2 = 0;
>
> memcpy(ses->auth_key.response + baselen, tiblob, tilen);
>
> @@ -706,7 +714,7 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
> }
>
> rc = crypto_shash_update(&ses->server->secmech.sdeschmacmd5->shash,
> - ses->auth_key.response + CIFS_SESS_KEY_SIZE,
> + ntlmv2->ntlmv2_hash,
> CIFS_HMAC_MD5_HASH_SIZE);
> if (rc) {
> cifs_dbg(VFS, "%s: Could not update with response\n", __func__);
> diff --git a/fs/cifs/cifspdu.h b/fs/cifs/cifspdu.h
> index 9e5ee34..33df36e 100644
> --- a/fs/cifs/cifspdu.h
> +++ b/fs/cifs/cifspdu.h
> @@ -697,7 +697,13 @@ struct ntlmssp2_name {
> } __attribute__((packed));
>
> struct ntlmv2_resp {
> - char ntlmv2_hash[CIFS_ENCPWD_SIZE];
> + union {
> + char ntlmv2_hash[CIFS_ENCPWD_SIZE];
> + struct {
> + __u8 reserved[8];
> + __u8 key[CIFS_SERVER_CHALLENGE_SIZE];
> + } __attribute__((packed)) challenge;
> + } __attribute__((packed));
> __le32 blob_signature;
> __u32 reserved;
> __le64 time;

(cc'ing Shirish since he wrote most of this code...)

Nice cleanup, I like it.

Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
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