Rechercher dans le manuel MySQL
6.2.7 Access Control, Stage 2: Request Verification
After you establish a connection, the server enters Stage 2 of
access control. For each request that you issue through that
connection, the server determines what operation you want to
perform, then checks whether you have sufficient privileges to do
so. This is where the privilege columns in the grant tables come
into play. These privileges can come from any of the
user
, db
,
tables_priv
, columns_priv
,
or procs_priv
tables. (You may find it helpful
to refer to Section 6.2.3, “Grant Tables”, which lists the
columns present in each of the grant tables.)
The user
table grants privileges that are
assigned to you on a global basis and that apply no matter what
the default database is. For example, if the
user
table grants you the
DELETE
privilege, you can delete
rows from any table in any database on the server host! It is wise
to grant privileges in the user
table only to
people who need them, such as database administrators. For other
users, you should leave all privileges in the
user
table set to 'N'
and
grant privileges at more specific levels only. You can grant
privileges for particular databases, tables, columns, or routines.
The db
table grants database-specific
privileges. Values in the scope columns of this table can take the
following forms:
A blank
User
value matches the anonymous user. A nonblank value matches literally; there are no wildcards in user names.The wildcard characters
%
and_
can be used in theHost
andDb
columns. These have the same meaning as for pattern-matching operations performed with theLIKE
operator. If you want to use either character literally when granting privileges, you must escape it with a backslash. For example, to include the underscore character (_
) as part of a database name, specify it as\_
in theGRANT
statement.A
'%'
or blankHost
value means “any host.”A
'%'
or blankDb
value means “any database.”
The server reads the db
table into memory and
sorts it at the same time that it reads the
user
table. The server sorts the
db
table based on the Host
,
Db
, and User
scope columns.
As with the user
table, sorting puts the
most-specific values first and least-specific values last, and
when the server looks for matching rows, it uses the first match
that it finds.
The tables_priv
,
columns_priv
, and procs_priv
tables grant table-specific, column-specific, and routine-specific
privileges. Values in the scope columns of these tables can take
the following forms:
The wildcard characters
%
and_
can be used in theHost
column. These have the same meaning as for pattern-matching operations performed with theLIKE
operator.A
'%'
or blankHost
value means “any host.”The
Db
,Table_name
,Column_name
, andRoutine_name
columns cannot contain wildcards or be blank.
The server sorts the tables_priv
,
columns_priv
, and procs_priv
tables based on the Host
,
Db
, and User
columns. This
is similar to db
table sorting, but simpler
because only the Host
column can contain
wildcards.
The server uses the sorted tables to verify each request that it
receives. For requests that require administrative privileges such
as SHUTDOWN
or
RELOAD
, the server checks only the
user
table row because that is the only table
that specifies administrative privileges. The server grants access
if the row permits the requested operation and denies access
otherwise. For example, if you want to execute mysqladmin
shutdown but your user
table row does
not grant the SHUTDOWN
privilege to
you, the server denies access without even checking the
db
table. (It contains no
Shutdown_priv
column, so there is no need to do
so.)
For database-related requests
(INSERT
,
UPDATE
, and so on), the server
first checks the user's global privileges by looking in the
user
table row. If the row permits the
requested operation, access is granted. If the global privileges
in the user
table are insufficient, the server
determines the user's database-specific privileges by checking the
db
table:
The server looks in the db
table for a match on
the Host
, Db
, and
User
columns. The Host
and
User
columns are matched to the connecting
user's host name and MySQL user name. The Db
column is matched to the database that the user wants to access.
If there is no row for the Host
and
User
, access is denied.
After determining the database-specific privileges granted by the
db
table rows, the server adds them to the
global privileges granted by the user
table. If
the result permits the requested operation, access is granted.
Otherwise, the server successively checks the user's table and
column privileges in the tables_priv
and
columns_priv
tables, adds those to the user's
privileges, and permits or denies access based on the result. For
stored-routine operations, the server uses the
procs_priv
table rather than
tables_priv
and
columns_priv
.
Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarized like this:
It may not be apparent why, if the global user
row privileges are initially found to be insufficient for the
requested operation, the server adds those privileges to the
database, table, and column privileges later. The reason is that a
request might require more than one type of privilege. For
example, if you execute an
INSERT INTO ...
SELECT
statement, you need both the
INSERT
and the
SELECT
privileges. Your privileges
might be such that the user
table row grants
one privilege and the db
table row grants the
other. In this case, you have the necessary privileges to perform
the request, but the server cannot tell that from either table by
itself; the privileges granted by the rows in both tables must be
combined.
Traduction non disponible
Le manuel MySQL n'est pas encore traduit en français sur l'infobrol. Seule la version anglaise est disponible pour l'instant.
Document créé le 26/06/2006, dernière modification le 26/10/2018
Source du document imprimé : https://www.gaudry.be/mysql-rf-request-access.html
L'infobrol est un site personnel dont le contenu n'engage que moi. Le texte est mis à disposition sous licence CreativeCommons(BY-NC-SA). Plus d'info sur les conditions d'utilisation et sur l'auteur.
Références
Ces références et liens indiquent des documents consultés lors de la rédaction de cette page, ou qui peuvent apporter un complément d'information, mais les auteurs de ces sources ne peuvent être tenus responsables du contenu de cette page.
L'auteur de ce site est seul responsable de la manière dont sont présentés ici les différents concepts, et des libertés qui sont prises avec les ouvrages de référence. N'oubliez pas que vous devez croiser les informations de sources multiples afin de diminuer les risques d'erreurs.