This patch fixes a leak that occurs when creating a new
thread-specific DNS resolver state object.
Essentially, each thread that calls gethostbyname() or getaddrinfo()
at least once will leak a small memory block. Another leak happens
anytime these functions are called after a change of the network
settings.
The leak is insignificant and hard to notice on typical programs.
However, netd tends to create one new thread for each DNS request
it processes, and quickly grows in size after a > 20 hours.
The same problem is seen in other system processes that tend to
create one thread per request too.
The leak occured becasue res_ninit() was called twice when creating
a new thread-specific DNS resolver state in _res_get_thread().
This function could not properly reset an existing thread and was
leaking a memory block.
The patch does two things:
- First, it fixes res_ninit() to prevent any leakage when resetting
the state of a given res_state instance.
- Second, it modifies the _res_get_thread() implementation to
make it more explicit, and avoid calling res_ninit() twice
in a row on first-time creation.
Fix for Bug 4089945, and Bug 4090857
Change-Id: Ie4831a8dbe82be8f07fce5ddd1d36bf95994f836
The problem was that the 'defdname' field of res_state structure
was not properly initialized in __res_vinit(). This field is used
to store the default domain name, which is normally build from
calling gethostname() (see line 549 of res_init.c).
Unfortunately, in the typical Android case, gethostname() returns
an error (the hostname is configured) and a random stack string is
used later to build the DNS search list (see lines 556+ in res_init.c)
For the sake of illustration, let's say the search list is set to
a random value like 'xWLK'.
The end result is that when trying to result an unknown domain name
(e.g. 'www.ptn'), the query fails then the resolver tries to make a
new query with the DNS search list path(s) appended (e.g. 'www.ptn.xWLK').
The patch simply initializes 'defdname' to an empty string to avoid
this when the net.dns.search system property is not set.
Also contains whitespace/formatting fixes
The current solution is to read the net.dns.search property,
and expand the list during the resolve initialization. In the
future, we could implement search list per process.
Update: refine the code accordingly.
Update: remove unnecessary code.
Update: remove the unused variable.
