Details
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Bug
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Status: Closed
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Major
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Resolution: Fixed
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None
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None
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Operating System: other
Platform: Other
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34490
Description
Problem Summary:
Currently, DBCP does not provide support for dealing with password changes when
using InstanceKeyDataSources. This means that when using a concrete
implementation of InstanceKeyDataSource, such as SharedPoolDataSource or
PerUserPoolDataSource, if a user changes his/her password, the entire connection
pool must be restarted for DBCP to recognize the new password. In the event the
connection pool is being managed by a container, such as Tomcat, it requires
restarting the container. Users have previously requested an ability to handle
these situations (see
http://mail-archives.eu.apache.org/mod_mbox/jakarta-commons-user/200405.mbox/%3C40B5F9DC.1080101@pandora.be%3E
and
http://mail-archives.eu.apache.org/mod_mbox/jakarta-commons-user/200405.mbox/%3c40ACA3DE.8080302@pandora.be%3e
for examples).
Proposed Patch:
The attached patch provides support for using the SharedPoolDataSource in
situations where user passwords may be changed. Support is provided by changing
UserPassKey and SharedPoolDataSource to use the concatenation of the username
and password as the key. In this way, after a user changes password, a
getConnection(String, String) method call will cause the pool to create a new
Connection using the new username and password. The Connection that was created
using the old username and password remains in the pool, where--assuming the
pool is set up to remove idle objects--it will be collected by the idle object
eviction thread or eventually (once the pool is full) be discarded according to
the LRU algorithm provided by the pool.
Other Solutions Considered:
In making this patch, I considered several other possible algorithms but chose
the implemented algorithm as the best combination of safety and ease of use.
And-as a bonus-it is a very unobtrusive solution. 
- The "public void close(String name)" method recommended by Dirk Verbeeck in
the first link above is relatively complex to implement in the case of a
SharedPoolDataSource (but would be much easier for a PerUserPoolDataSource, as
he suggested). In the case of a SharedPoolDataSource, it's possible that
multiple Connections exist for the specified user, in which case
SharedPoolDataSource would have to provide logic to deal with the cases where
one or more existing connections for the user are checked out at the time the
method is called--not to mention the logic required to find all existing
connections and close them without needlessly opening new connections (since all
users share the same pool in a SharedPoolDataSource instead of having a pool per
user as in PerUserPoolDataSource).
- Adding a method "public void getConnection(String username, String password,
boolean closeAndReconnectOnPasswordMismatch)" has similar problems with the
possibility of the existence of multiple open connections for the given
username. If only the current connection is closed, we may be leaving
connections that are associated with the old password in the pool; therefore,
the application would need to use the closeAndReconnect functionality in
most-if not all-cases where a connection is required. If all connections are
closed, we have the same situation described above.
Furthermore, neither of the above methods is a part of the DataSource interface;
and, therefore, both would require the application to downcast to the
appropriate DBCP type to make the method call. For all practical purposes, this
negates the benefits of using an interface in the first place.
Additionally, adding new methods as above requires the application to know when
the user has changed his/her password, and provides a potential failure mode
when the user changes his/her password through an external application (i.e.
directly on the database or using some other application). Although it is
possible for the application to catch the plain-vanilla SQLException thrown by
the getConnection(String, String) method of InstanceKeyDataSource and parse the
exception message looking for the expected text ("Given password did not match
password used to create the PooledConnection."), doing so is not at all an
elegant solution. Even if a new PasswordChangedException (which extends
SQLException) were created, the application would then need to downcast the
DataSource to make the appropriate call, so the previously mentioned problems
with the solution apply.
Also, both of the new methods allow a Denial-of-Service-type attack against the
connection pool wherein a user may prevent the connection pool from reusing
connections by forcing it to close connections and attempt a reconnect when
given an incorrect password. Depending on the application design, this weakness
could be exploited from a login page, knowing only valid usernames. The
proposed solution does not suffer from this problem as the existing connections
are kept, so a user requesting a connection with a bad password would simply
cause DBCP to attempt to make a connection that the database would refuse
because of an invalid password.
- Checking the given password in the getPooledConnectionAndInfo( ) method and,
if different from the originally given password, attempting to connect to the
database with the new username/password combination and changing the password
associated with the UserPassKey after a successful connection would also work,
but requires duplicating the password check done by the InstanceKeyDataSource in
subclasses wanting to support use after password changes (or removing the check
from InstanceKeyDataSource and requiring subclasses to handle the situation
appropriately). Furthermore, since database behavior regarding usability of
Connections after a password change is database-dependent, we cannot be sure
that the existing connections-which were created with the old password-are
still valid, so this approach would require users to run a validation query.
Therefore, it seems more reasonable to simply leave the existing connections and
let them be evicted or thrown away when the pool becomes full.
Design Decisions for the Attached Patch:
The first required change was to modify the hashCode() method in the UserPassKey
class to create a hash based upon both the username and password. This was done
simply by concatenating username and password and returning the hashCode of the
combined String. If the username is null, 0 is returned. If the password is
null but the username is not, the String "null" will be concatenated to the
username and the hashCode of the combined String will be returned. Although it
would have been prettier to only append the password if it is not null, the
additional logic and extra processing time required for the change did not seem
worthwhile.
Next, the getUserPassKey(String username, String password) method was modified
to ensure the username and password were used as the key for the Map. In the
event that username and password are both null, the key will be "nullnull".
Similarly, the String "null" will be used for the part associated with username
or password if one is null. This means that we will never use a null value for
a key; however, the effect is the same--since the hashCode() of the String
"nullnull" will always be the same, we'll have only one entry for the
UserPassKey having null username and password. We only create a new Map entry
when either username or password is different (as opposed to before, where we
only create a new entry when username is different).
Although using the password in the key may be considered to have security
implications (as a hash of username and password could be considered a password
equivalent), the data will only be available to the application--which, itself,
is handling the password. Furthermore, since the UserPassKey is storing the
unencoded password, and since the UserPassKey's toString() method returns the
unencoded username and password, the proposed patch does not seem to negatively
impact security of the class.
The patch also modifies testIncorrectPassword() in TestSharedPoolDataSource.
After the patch is applied, the SharedPoolDataSource will attempt to connect
with the new (incorrect) password. The DataSource throws a SQLNestedException
("Could not retrieve connection info from pool") chained to a SQLException ("x
is not the correct password for u1. The correct password is p1").
While the existing patch only applies to the SharedPoolDataSource, I would be
happy to provide a similar patch for the PerUserPoolDataSource (for the reasons
given above, I feel this approach is also the best approach for the
PerUserPoolDataSource). If interested, let me know and I'll file a patch on
another bug report.