cifs: improve symlink handling for smb2+

When creating inode for symlink, the client used to send below
requests to fill it in:

    * create+query_info+close (STATUS_STOPPED_ON_SYMLINK)
    * create(+reparse_flag)+query_info+close (set file attrs)
    * create+ioctl(get_reparse)+close (query reparse tag)

and then for every access to the symlink dentry, the ->link() method
would send another:

    * create+ioctl(get_reparse)+close (parse symlink)

So, in order to improve:

    (i) Get rid of unnecessary roundtrips and then resolve symlinks as
	follows:

        * create+query_info+close (STATUS_STOPPED_ON_SYMLINK +
	                           parse symlink + get reparse tag)
        * create(+reparse_flag)+query_info+close (set file attrs)

    (ii) Set the resolved symlink target directly in inode->i_link and
         use simple_get_link() for ->link() to simply return it.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 106 insertions, 21 deletions

diff --git a/fs/cifs/smb2file.c b/fs/cifs/smb2file.c
index 9dfd2dd612c2..4992b43616a7 100644
--- a/fs/cifs/smb2file.c
+++ b/fs/cifs/smb2file.c
@@ -20,40 +20,125 @@
 #include "cifs_unicode.h"
 #include "fscache.h"
 #include "smb2proto.h"
+#include "smb2status.h"
 
-int
-smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms,
-	       __u32 *oplock, FILE_ALL_INFO *buf)
+static struct smb2_symlink_err_rsp *symlink_data(const struct kvec *iov)
+{
+	struct smb2_err_rsp *err = iov->iov_base;
+	struct smb2_symlink_err_rsp *sym = ERR_PTR(-EINVAL);
+	u32 len;
+
+	if (err->ErrorContextCount) {
+		struct smb2_error_context_rsp *p, *end;
+
+		len = (u32)err->ErrorContextCount * (offsetof(struct smb2_error_context_rsp,
+							      ErrorContextData) +
+						     sizeof(struct smb2_symlink_err_rsp));
+		if (le32_to_cpu(err->ByteCount) < len || iov->iov_len < len + sizeof(*err))
+			return ERR_PTR(-EINVAL);
+
+		p = (struct smb2_error_context_rsp *)err->ErrorData;
+		end = (struct smb2_error_context_rsp *)((u8 *)err + iov->iov_len);
+		do {
+			if (le32_to_cpu(p->ErrorId) == SMB2_ERROR_ID_DEFAULT) {
+				sym = (struct smb2_symlink_err_rsp *)&p->ErrorContextData;
+				break;
+			}
+			cifs_dbg(FYI, "%s: skipping unhandled error context: 0x%x\n",
+				 __func__, le32_to_cpu(p->ErrorId));
+
+			len = ALIGN(le32_to_cpu(p->ErrorDataLength), 8);
+			p = (struct smb2_error_context_rsp *)((u8 *)&p->ErrorContextData + len);
+		} while (p < end);
+	} else if (le32_to_cpu(err->ByteCount) >= sizeof(*sym) &&
+		   iov->iov_len >= SMB2_SYMLINK_STRUCT_SIZE) {
+		sym = (struct smb2_symlink_err_rsp *)err->ErrorData;
+	}
+
+	if (!IS_ERR(sym) && (le32_to_cpu(sym->SymLinkErrorTag) != SYMLINK_ERROR_TAG ||
+			     le32_to_cpu(sym->ReparseTag) != IO_REPARSE_TAG_SYMLINK))
+		sym = ERR_PTR(-EINVAL);
+
+	return sym;
+}
+
+int smb2_parse_symlink_response(struct cifs_sb_info *cifs_sb, const struct kvec *iov, char **path)
+{
+	struct smb2_symlink_err_rsp *sym;
+	unsigned int sub_offs, sub_len;
+	unsigned int print_offs, print_len;
+	char *s;
+
+	if (!cifs_sb || !iov || !iov->iov_base || !iov->iov_len || !path)
+		return -EINVAL;
+
+	sym = symlink_data(iov);
+	if (IS_ERR(sym))
+		return PTR_ERR(sym);
+
+	sub_len = le16_to_cpu(sym->SubstituteNameLength);
+	sub_offs = le16_to_cpu(sym->SubstituteNameOffset);
+	print_len = le16_to_cpu(sym->PrintNameLength);
+	print_offs = le16_to_cpu(sym->PrintNameOffset);
+
+	if (iov->iov_len < SMB2_SYMLINK_STRUCT_SIZE + sub_offs + sub_len ||
+	    iov->iov_len < SMB2_SYMLINK_STRUCT_SIZE + print_offs + print_len)
+		return -EINVAL;
+
+	s = cifs_strndup_from_utf16((char *)sym->PathBuffer + sub_offs, sub_len, true,
+				    cifs_sb->local_nls);
+	if (!s)
+		return -ENOMEM;
+	convert_delimiter(s, '/');
+	cifs_dbg(FYI, "%s: symlink target: %s\n", __func__, s);
+
+	*path = s;
+	return 0;
+}
+
+int smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms, __u32 *oplock, void *buf)
 {
 	int rc;
 	__le16 *smb2_path;
-	struct smb2_file_all_info *smb2_data = NULL;
 	__u8 smb2_oplock;
+	struct cifs_open_info_data *data = buf;
+	struct smb2_file_all_info file_info = {};
+	struct smb2_file_all_info *smb2_data = data ? &file_info : NULL;
+	struct kvec err_iov = {};
+	int err_buftype = CIFS_NO_BUFFER;
 	struct cifs_fid *fid = oparms->fid;
 	struct network_resiliency_req nr_ioctl_req;
 
 	smb2_path = cifs_convert_path_to_utf16(oparms->path, oparms->cifs_sb);
-	if (smb2_path == NULL) {
-		rc = -ENOMEM;
-		goto out;
-	}
-
-	smb2_data = kzalloc(sizeof(struct smb2_file_all_info) + PATH_MAX * 2,
-			    GFP_KERNEL);
-	if (smb2_data == NULL) {
-		rc = -ENOMEM;
-		goto out;
-	}
+	if (smb2_path == NULL)
+		return -ENOMEM;
 
 	oparms->desired_access |= FILE_READ_ATTRIBUTES;
 	smb2_oplock = SMB2_OPLOCK_LEVEL_BATCH;
 
-	rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data, NULL,
-		       NULL, NULL);
+	rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data, NULL, &err_iov,
+		       &err_buftype);
+	if (rc && data) {
+		struct smb2_hdr *hdr = err_iov.iov_base;
+
+		if (unlikely(!err_iov.iov_base || err_buftype == CIFS_NO_BUFFER))
+			rc = -ENOMEM;
+		else if (hdr->Status == STATUS_STOPPED_ON_SYMLINK && oparms->cifs_sb) {
+			rc = smb2_parse_symlink_response(oparms->cifs_sb, &err_iov,
+							 &data->symlink_target);
+			if (!rc) {
+				memset(smb2_data, 0, sizeof(*smb2_data));
+				oparms->create_options |= OPEN_REPARSE_POINT;
+				rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data,
+					       NULL, NULL, NULL);
+				oparms->create_options &= ~OPEN_REPARSE_POINT;
+			}
+		}
+	}
+
 	if (rc)
 		goto out;
 
-
 	if (oparms->tcon->use_resilient) {
 		/* default timeout is 0, servers pick default (120 seconds) */
 		nr_ioctl_req.Timeout =
@@ -73,7 +158,7 @@ smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms,
 		rc = 0;
 	}
 
-	if (buf) {
+	if (smb2_data) {
 		/* if open response does not have IndexNumber field - get it */
 		if (smb2_data->IndexNumber == 0) {
 			rc = SMB2_get_srv_num(xid, oparms->tcon,
@@ -89,12 +174,12 @@ smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms,
 				rc = 0;
 			}
 		}
-		move_smb2_info_to_cifs(buf, smb2_data);
+		memcpy(&data->fi, smb2_data, sizeof(data->fi));
 	}
 
 	*oplock = smb2_oplock;
 out:
-	kfree(smb2_data);
+	free_rsp_buf(err_buftype, err_iov.iov_base);
 	kfree(smb2_path);
 	return rc;
 }