In the negotiate protocol preauth context, the server is not required
to populate the salt (although it is recommended, and done by most
servers) so do not warn on mount if the salt is not 32 bytes, but
instead simply check that the preauth context is the minimum size
and that the salt would not overflow the buffer length.

CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/smb2pdu.c |  7 +++++--
 fs/cifs/smb2pdu.h | 14 +++++++++++---
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index acb72705062d..8d572dcf330a 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -427,8 +427,8 @@ build_preauth_ctxt(struct smb2_preauth_neg_context
*pneg_ctxt)
  pneg_ctxt->ContextType = SMB2_PREAUTH_INTEGRITY_CAPABILITIES;
  pneg_ctxt->DataLength = cpu_to_le16(38);
  pneg_ctxt->HashAlgorithmCount = cpu_to_le16(1);
- pneg_ctxt->SaltLength = cpu_to_le16(SMB311_SALT_SIZE);
- get_random_bytes(pneg_ctxt->Salt, SMB311_SALT_SIZE);
+ pneg_ctxt->SaltLength = cpu_to_le16(SMB311_CLIENT_SALT_SIZE);
+ get_random_bytes(pneg_ctxt->Salt, SMB311_CLIENT_SALT_SIZE);
  pneg_ctxt->HashAlgorithms = SMB2_PREAUTH_INTEGRITY_SHA512;
 }

@@ -566,6 +566,9 @@ static void decode_preauth_context(struct
smb2_preauth_neg_context *ctxt)
  if (len < MIN_PREAUTH_CTXT_DATA_LEN) {
  pr_warn_once("server sent bad preauth context\n");
  return;
+ } else if (len < MIN_PREAUTH_CTXT_DATA_LEN + le16_to_cpu(ctxt->SaltLength)) {
+ pr_warn_once("server sent invalid SaltLength\n");
+ return;
  }
  if (le16_to_cpu(ctxt->HashAlgorithmCount) != 1)
  pr_warn_once("Invalid SMB3 hash algorithm count\n");
diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index fa57b03ca98c..de3127a6fc34 100644
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -333,12 +333,20 @@ struct smb2_neg_context {
  /* Followed by array of data */
 } __packed;

-#define SMB311_SALT_SIZE 32
+#define SMB311_CLIENT_SALT_SIZE 32
 /* Hash Algorithm Types */
 #define SMB2_PREAUTH_INTEGRITY_SHA512 cpu_to_le16(0x0001)
 #define SMB2_PREAUTH_HASH_SIZE 64

-#define MIN_PREAUTH_CTXT_DATA_LEN (SMB311_SALT_SIZE + 6)
+/*
+ * SaltLength that the server send can be zero, so the only three required
+ * fields (all __le16) end up six bytes total, so the minimum context data len
+ * in the response is six.
+ * The three required are: HashAlgorithmCount, SaltLength, and 1 HashAlgorithm
+ * Although most servers send a SaltLength of 32 bytes, technically it is
+ * optional.
+ */
+#define MIN_PREAUTH_CTXT_DATA_LEN 6
 struct smb2_preauth_neg_context {
  __le16 ContextType; /* 1 */
  __le16 DataLength;
@@ -346,7 +354,7 @@ struct smb2_preauth_neg_context {
  __le16 HashAlgorithmCount; /* 1 */
  __le16 SaltLength;
  __le16 HashAlgorithms; /* HashAlgorithms[0] since only one defined */
- __u8 Salt[SMB311_SALT_SIZE];
+ __u8 Salt[SMB311_CLIENT_SALT_SIZE];
 } __packed;

 /* Encryption Algorithms Ciphers */


-- 
Thanks,

Steve