2 files changed, 73 insertions, 5 deletions

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 3fdc6a41b304..9fd56b0acd7e 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -2372,6 +2372,41 @@ smb2_get_dfs_refer(const unsigned int xid, struct cifs_ses *ses,
         kfree(dfs_rsp);
         return rc;
 }
+
+static int
+parse_reparse_symlink(struct reparse_symlink_data_buffer *symlink_buf,
+                      u32 plen, char **target_path,
+                      struct cifs_sb_info *cifs_sb)
+{
+        unsigned int sub_len;
+        unsigned int sub_offset;
+
+        /* We only handle Symbolic Link : MS-FSCC 2.1.2.4 */
+        if (le32_to_cpu(symlink_buf->ReparseTag) != IO_REPARSE_TAG_SYMLINK) {
+                cifs_dbg(VFS, "srv returned invalid symlink buffer\n");
+                return -EIO;
+        }
+
+        sub_offset = le16_to_cpu(symlink_buf->SubstituteNameOffset);
+        sub_len = le16_to_cpu(symlink_buf->SubstituteNameLength);
+        if (sub_offset + 20 > plen ||
+            sub_offset + sub_len + 20 > plen) {
+                cifs_dbg(VFS, "srv returned malformed symlink buffer\n");
+                return -EIO;
+        }
+
+        *target_path = cifs_strndup_from_utf16(
+                                symlink_buf->PathBuffer + sub_offset,
+                                sub_len, true, cifs_sb->local_nls);
+        if (!(*target_path))
+                return -ENOMEM;
+
+        convert_delimiter(*target_path, '/');
+        cifs_dbg(FYI, "%s: target path: %s\n", __func__, *target_path);
+
+        return 0;
+}
+
 #define SMB2_SYMLINK_STRUCT_SIZE \
         (sizeof(struct smb2_err_rsp) - 1 + sizeof(struct smb2_symlink_err_rsp))
 
@@ -2401,11 +2436,13 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
         struct kvec close_iov[1];
         struct smb2_create_rsp *create_rsp;
         struct smb2_ioctl_rsp *ioctl_rsp;
-        char *ioctl_buf;
+        struct reparse_data_buffer *reparse_buf;
         u32 plen;
 
         cifs_dbg(FYI, "%s: path: %s\n", __func__, full_path);
 
+        *target_path = NULL;
+
         if (smb3_encryption_required(tcon))
                 flags |= CIFS_TRANSFORM_REQ;
 
@@ -2483,17 +2520,36 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
         if ((rc == 0) && (is_reparse_point)) {
                 /* See MS-FSCC 2.3.23 */
 
-                ioctl_buf = (char *)ioctl_rsp + le32_to_cpu(ioctl_rsp->OutputOffset);
+                reparse_buf = (struct reparse_data_buffer *)
+                        ((char *)ioctl_rsp +
+                         le32_to_cpu(ioctl_rsp->OutputOffset));
                 plen = le32_to_cpu(ioctl_rsp->OutputCount);
 
                 if (plen + le32_to_cpu(ioctl_rsp->OutputOffset) >
                     rsp_iov[1].iov_len) {
-                        cifs_dbg(VFS, "srv returned invalid ioctl length: %d\n", plen);
+                        cifs_dbg(VFS, "srv returned invalid ioctl len: %d\n",
+                                 plen);
+                        rc = -EIO;
+                        goto querty_exit;
+                }
+
+                if (plen < 8) {
+                        cifs_dbg(VFS, "reparse buffer is too small. Must be "
+                                 "at least 8 bytes but was %d\n", plen);
+                        rc = -EIO;
+                        goto querty_exit;
+                }
+
+                if (plen < le16_to_cpu(reparse_buf->ReparseDataLength) + 8) {
+                        cifs_dbg(VFS, "srv returned invalid reparse buf "
+                                 "length: %d\n", plen);
                         rc = -EIO;
                         goto querty_exit;
                 }
 
-                /* Do stuff with ioctl_buf/plen */
+                rc = parse_reparse_symlink(
+                        (struct reparse_symlink_data_buffer *)reparse_buf,
+                        plen, target_path, cifs_sb);
                 goto querty_exit;
         }
 
diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index c7d5813bebd8..858353d20c39 100644
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -914,7 +914,19 @@ struct reparse_mount_point_data_buffer {
         __u8    PathBuffer[0]; /* Variable Length */
 } __packed;
 
-/* See MS-FSCC 2.1.2.4 and cifspdu.h for struct reparse_symlink_data */
+#define SYMLINK_FLAG_RELATIVE 0x00000001
+
+struct reparse_symlink_data_buffer {
+        __le32  ReparseTag;
+        __le16  ReparseDataLength;
+        __u16   Reserved;
+        __le16  SubstituteNameOffset;
+        __le16  SubstituteNameLength;
+        __le16  PrintNameOffset;
+        __le16  PrintNameLength;
+        __le32  Flags;
+        __u8    PathBuffer[0]; /* Variable Length */
+} __packed;
 
 /* See MS-FSCC 2.1.2.6 and cifspdu.h for struct reparse_posix_data */