From: Pali Rohár pali@kernel.org
[ Upstream commit 89381c72d52094988e11d23ef24a00066a0fa458 ]
[MS-CIFS] specification in section 2.2.4.53.1 where is described SMB_COM_SESSION_SETUP_ANDX Request, for SessionKey field says:
The client MUST set this field to be equal to the SessionKey field in the SMB_COM_NEGOTIATE Response for this SMB connection.
Linux SMB client currently set this field to zero. This is working fine against Windows NT SMB servers thanks to [MS-CIFS] product behavior <94>:
Windows NT Server ignores the client's SessionKey.
For compatibility with [MS-CIFS], set this SessionKey field in Session Setup Request to value retrieved from Negotiate response.
Signed-off-by: Pali Rohár pali@kernel.org Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my comprehensive analysis of both the commit message and code changes, examining the current kernel tree context: **YES** ## Extensive Analysis ### **Nature of the Fix** This is a **specification compliance fix** for SMB1 protocol handling. The commit addresses a clear violation of the MS-CIFS specification section 2.2.4.53.1, which mandates that the SessionKey field in SMB_COM_SESSION_SETUP_ANDX Request must be set to the value from the SMB_COM_NEGOTIATE Response. ### **Code Changes Analysis** **1. Structural Changes (Low Risk)** - **cifsglob.h**: Adds `__le32 session_key_id` to `TCP_Server_Info` structure - minimal ABI impact as this is kernel-internal - **cifspdu.h**: Corrects endianness annotations from `__u32` to `__le32` - pure annotation fix, no behavioral change **2. Functional Changes (Contained and Safe)** - **cifssmb.c**: Captures SessionKey from negotiate response (`server->session_key_id = pSMBr->SessionKey`) - simple field assignment - **sess.c**: Sets SessionKey in session setup request (`pSMB->req.SessionKey = server->session_key_id`) - follows specification requirement ### **Risk Assessment** **Minimal Regression Risk:** - Changes are isolated to SMB1 legacy protocol code - Current behavior (setting SessionKey to zero) works with Windows NT due to MS- CIFS product behavior <94> - New behavior follows specification exactly, improving compatibility with non-Windows SMB1 servers - No security implications - purely a protocol compliance improvement **Code Maturity:** - SMB1 session setup code is very mature and stable - Limited recent changes in this area except compatibility fixes - Well- understood code path with clear specification backing ### **Backport Suitability Criteria Met** **1. Important Bug Fix:** ✅ Fixes protocol specification violation that could cause compatibility issues with strict SMB1 implementations **2. Small and Contained:** ✅ Four minimal changes across related files, all implementing the same specification requirement **3. Clear Side Effects:** ✅ No side effects beyond fixing the specification compliance issue **4. No Architectural Changes:** ✅ Simple field additions and assignments, no structural changes **5. Non- Critical Subsystem:** ✅ Legacy SMB1 protocol code, deprecated since 2017 **6. Minimal Risk:** ✅ Maintains backward compatibility while improving forward compatibility **7. Stable Tree Rules Compliance:** ✅ Important compatibility bugfix with minimal regression risk ### **Comparison to Similar Commits** This commit closely matches the pattern of **Similar Commit #3** and **Similar Commit #5** (both marked YES for backporting): - Protocol compliance improvements - Session setup related fixes - Clear specification backing - Minimal, contained changes - Authored by maintainers (Steve French involvement) ### **Conclusion** This commit represents an ideal stable backport candidate: a clear specification compliance fix with minimal code changes, no security implications, and improvement in interoperability. The fix ensures Linux kernel SMB client properly follows MS-CIFS specification, which is valuable for enterprise environments using diverse SMB1 server implementations.
fs/smb/client/cifsglob.h | 1 + fs/smb/client/cifspdu.h | 6 +++--- fs/smb/client/cifssmb.c | 1 + fs/smb/client/sess.c | 1 + 4 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h index 39117343b703f..1f3451202fe8d 100644 --- a/fs/smb/client/cifsglob.h +++ b/fs/smb/client/cifsglob.h @@ -739,6 +739,7 @@ struct TCP_Server_Info { char workstation_RFC1001_name[RFC1001_NAME_LEN_WITH_NULL]; __u32 sequence_number; /* for signing, protected by srv_mutex */ __u32 reconnect_instance; /* incremented on each reconnect */ + __le32 session_key_id; /* retrieved from negotiate response and send in session setup request */ struct session_key session_key; unsigned long lstrp; /* when we got last response from this server */ struct cifs_secmech secmech; /* crypto sec mech functs, descriptors */ diff --git a/fs/smb/client/cifspdu.h b/fs/smb/client/cifspdu.h index ca33f6cd6a800..763178b774542 100644 --- a/fs/smb/client/cifspdu.h +++ b/fs/smb/client/cifspdu.h @@ -557,7 +557,7 @@ typedef union smb_com_session_setup_andx { __le16 MaxBufferSize; __le16 MaxMpxCount; __le16 VcNumber; - __u32 SessionKey; + __le32 SessionKey; __le16 SecurityBlobLength; __u32 Reserved; __le32 Capabilities; /* see below */ @@ -576,7 +576,7 @@ typedef union smb_com_session_setup_andx { __le16 MaxBufferSize; __le16 MaxMpxCount; __le16 VcNumber; - __u32 SessionKey; + __le32 SessionKey; __le16 CaseInsensitivePasswordLength; /* ASCII password len */ __le16 CaseSensitivePasswordLength; /* Unicode password length*/ __u32 Reserved; /* see below */ @@ -614,7 +614,7 @@ typedef union smb_com_session_setup_andx { __le16 MaxBufferSize; __le16 MaxMpxCount; __le16 VcNumber; - __u32 SessionKey; + __le32 SessionKey; __le16 PasswordLength; __u32 Reserved; /* encrypt key len and offset */ __le16 ByteCount; diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c index b91184ebce02c..096ea62e87ea9 100644 --- a/fs/smb/client/cifssmb.c +++ b/fs/smb/client/cifssmb.c @@ -479,6 +479,7 @@ CIFSSMBNegotiate(const unsigned int xid, server->max_rw = le32_to_cpu(pSMBr->MaxRawSize); cifs_dbg(NOISY, "Max buf = %d\n", ses->server->maxBuf); server->capabilities = le32_to_cpu(pSMBr->Capabilities); + server->session_key_id = pSMBr->SessionKey; server->timeAdj = (int)(__s16)le16_to_cpu(pSMBr->ServerTimeZone); server->timeAdj *= 60;
diff --git a/fs/smb/client/sess.c b/fs/smb/client/sess.c index f04922eb45d4c..a7ece67ee9630 100644 --- a/fs/smb/client/sess.c +++ b/fs/smb/client/sess.c @@ -680,6 +680,7 @@ static __u32 cifs_ssetup_hdr(struct cifs_ses *ses, USHRT_MAX)); pSMB->req.MaxMpxCount = cpu_to_le16(server->maxReq); pSMB->req.VcNumber = cpu_to_le16(1); + pSMB->req.SessionKey = server->session_key_id;
/* Now no need to set SMBFLG_CASELESS or obsolete CANONICAL PATH */