smb3: Fix enumerating snapshots to Azure

Some servers (see MS-SMB2 protocol specification
section 3.3.5.15.1) expect that the FSCTL enumerate snapshots
is done twice, with the first query having EXACTLY the minimum
size response buffer requested (16 bytes) which refreshes
the snapshot list (otherwise that and subsequent queries get
an empty list returned).  So had to add code to set
the maximum response size differently for the first snapshot
query (which gets the size needed for the second query which
contains the actual list of snapshots).

Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
CC: Stable <stable@vger.kernel.org> # 4.19+

1 files changed, 22 insertions, 13 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 21ac19ff19cb..0dc66f36ff5b 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1002,7 +1002,8 @@ int smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon *tcon)
 
 	rc = SMB2_ioctl(xid, tcon, NO_FILE_ID, NO_FILE_ID,
 		FSCTL_VALIDATE_NEGOTIATE_INFO, true /* is_fsctl */,
-		(char *)pneg_inbuf, inbuflen, (char **)&pneg_rsp, &rsplen);
+		(char *)pneg_inbuf, inbuflen, CIFSMaxBufSize,
+		(char **)&pneg_rsp, &rsplen);
 	if (rc == -EOPNOTSUPP) {
 		/*
 		 * Old Windows versions or Netapp SMB server can return
@@ -2478,7 +2479,8 @@ creat_exit:
 int
 SMB2_ioctl_init(struct cifs_tcon *tcon, struct smb_rqst *rqst,
 		u64 persistent_fid, u64 volatile_fid, u32 opcode,
-		bool is_fsctl, char *in_data, u32 indatalen)
+		bool is_fsctl, char *in_data, u32 indatalen,
+		__u32 max_response_size)
 {
 	struct smb2_ioctl_req *req;
 	struct kvec *iov = rqst->rq_iov;
@@ -2520,16 +2522,21 @@ SMB2_ioctl_init(struct cifs_tcon *tcon, struct smb_rqst *rqst,
 	req->OutputCount = 0; /* MBZ */
 
 	/*
-	 * Could increase MaxOutputResponse, but that would require more
-	 * than one credit. Windows typically sets this smaller, but for some
+	 * In most cases max_response_size is set to 16K (CIFSMaxBufSize)
+	 * We Could increase default MaxOutputResponse, but that could require
+	 * more credits. Windows typically sets this smaller, but for some
 	 * ioctls it may be useful to allow server to send more. No point
 	 * limiting what the server can send as long as fits in one credit
-	 * Unfortunately - we can not handle more than CIFS_MAX_MSG_SIZE
-	 * (by default, note that it can be overridden to make max larger)
-	 * in responses (except for read responses which can be bigger.
-	 * We may want to bump this limit up
+	 * We can not handle more than CIFS_MAX_BUF_SIZE yet but may want
+	 * to increase this limit up in the future.
+	 * Note that for snapshot queries that servers like Azure expect that
+	 * the first query be minimal size (and just used to get the number/size
+	 * of previous versions) so response size must be specified as EXACTLY
+	 * sizeof(struct snapshot_array) which is 16 when rounded up to multiple
+	 * of eight bytes.  Currently that is the only case where we set max
+	 * response size smaller.
 	 */
-	req->MaxOutputResponse = cpu_to_le32(CIFSMaxBufSize);
+	req->MaxOutputResponse = cpu_to_le32(max_response_size);
 
 	if (is_fsctl)
 		req->Flags = cpu_to_le32(SMB2_0_IOCTL_IS_FSCTL);
@@ -2550,13 +2557,14 @@ SMB2_ioctl_free(struct smb_rqst *rqst)
 		cifs_small_buf_release(rqst->rq_iov[0].iov_base); /* request */
 }
 
+
 /*
  *	SMB2 IOCTL is used for both IOCTLs and FSCTLs
  */
 int
 SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	   u64 volatile_fid, u32 opcode, bool is_fsctl,
-	   char *in_data, u32 indatalen,
+	   char *in_data, u32 indatalen, u32 max_out_data_len,
 	   char **out_data, u32 *plen /* returned data len */)
 {
 	struct smb_rqst rqst;
@@ -2593,8 +2601,8 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	rqst.rq_iov = iov;
 	rqst.rq_nvec = SMB2_IOCTL_IOV_SIZE;
 
-	rc = SMB2_ioctl_init(tcon, &rqst, persistent_fid, volatile_fid,
-			     opcode, is_fsctl, in_data, indatalen);
+	rc = SMB2_ioctl_init(tcon, &rqst, persistent_fid, volatile_fid, opcode,
+			     is_fsctl, in_data, indatalen, max_out_data_len);
 	if (rc)
 		goto ioctl_exit;
 
@@ -2672,7 +2680,8 @@ SMB2_set_compression(const unsigned int xid, struct cifs_tcon *tcon,
 	rc = SMB2_ioctl(xid, tcon, persistent_fid, volatile_fid,
 			FSCTL_SET_COMPRESSION, true /* is_fsctl */,
 			(char *)&fsctl_input /* data input */,
-			2 /* in data len */, &ret_data /* out data */, NULL);
+			2 /* in data len */, CIFSMaxBufSize /* max out data */,
+			&ret_data /* out data */, NULL);
 
 	cifs_dbg(FYI, "set compression rc %d\n", rc);