CIFS: Fix a possible invalid memory access in smb2_query_symlink()

During following a symbolic link we received err_buf from SMB2_open().
While the validity of SMB2 error response is checked previously
in smb2_check_message() a symbolic link payload is not checked at all.
Fix it by adding such checks.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 29 insertions, 1 deletions

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 527d1ac8583b..d203c0329626 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1044,6 +1044,9 @@ smb2_new_lease_key(struct cifs_fid *fid)
         get_random_bytes(fid->lease_key, SMB2_LEASE_KEY_SIZE);
 }
 
+#define SMB2_SYMLINK_STRUCT_SIZE \
+        (sizeof(struct smb2_err_rsp) - 1 + sizeof(struct smb2_symlink_err_rsp))
+
 static int
 smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
                    const char *full_path, char **target_path,
@@ -1056,7 +1059,10 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
         struct cifs_fid fid;
         struct smb2_err_rsp *err_buf = NULL;
         struct smb2_symlink_err_rsp *symlink;
-        unsigned int sub_len, sub_offset;
+        unsigned int sub_len;
+        unsigned int sub_offset;
+        unsigned int print_len;
+        unsigned int print_offset;
 
         cifs_dbg(FYI, "%s: path: %s\n", __func__, full_path);
 
@@ -1077,11 +1083,33 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
                 kfree(utf16_path);
                 return -ENOENT;
         }
+
+        if (le32_to_cpu(err_buf->ByteCount) < sizeof(struct smb2_symlink_err_rsp) ||
+            get_rfc1002_length(err_buf) + 4 < SMB2_SYMLINK_STRUCT_SIZE) {
+                kfree(utf16_path);
+                return -ENOENT;
+        }
+
         /* open must fail on symlink - reset rc */
         rc = 0;
         symlink = (struct smb2_symlink_err_rsp *)err_buf->ErrorData;
         sub_len = le16_to_cpu(symlink->SubstituteNameLength);
         sub_offset = le16_to_cpu(symlink->SubstituteNameOffset);
+        print_len = le16_to_cpu(symlink->PrintNameLength);
+        print_offset = le16_to_cpu(symlink->PrintNameOffset);
+
+        if (get_rfc1002_length(err_buf) + 4 <
+                        SMB2_SYMLINK_STRUCT_SIZE + sub_offset + sub_len) {
+                kfree(utf16_path);
+                return -ENOENT;
+        }
+
+        if (get_rfc1002_length(err_buf) + 4 <
+                        SMB2_SYMLINK_STRUCT_SIZE + print_offset + print_len) {
+                kfree(utf16_path);
+                return -ENOENT;
+        }
+
         *target_path = cifs_strndup_from_utf16(
                                 (char *)symlink->PathBuffer + sub_offset,
                                 sub_len, true, cifs_sb->local_nls);