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  1. Fix use-after-free issue in slot synchronization.

  1. Fix use of variable after pfree

    Shlok Kyal <shlok.kyal.oss@gmail.com> — 2025-09-02T07:32:23Z

    Hi,

While going through the code of the slot sync worker, I found that in
functions ReplSlotSyncWorkerMain and pg_sync_replication_slots the
variable app_name.data is being used after it is freed.

We can get logs as following:
2025-09-02 12:26:48.520 IST [3908359] ERROR:  synchronization worker
"" could not connect to the primary server: connection to server at
"localhost" (127.0.0.1), port 5432 failed: Connection refused
        Is the server running on that host and accepting TCP/IP connections?

I have moved the pfree(app_data.name) after its usage.

This change was introduced in PG_18.
The patch applies in the HEAD and REL_18_STABLE branches.

Thanks,
Shlok Kyal

  2. Re: Fix use of variable after pfree

    Amit Kapila <amit.kapila16@gmail.com> — 2025-09-02T07:42:49Z

    On Tue, Sep 2, 2025 at 1:02 PM Shlok Kyal <shlok.kyal.oss@gmail.com> wrote:
>
> Hi,
>
> While going through the code of the slot sync worker, I found that in
> functions ReplSlotSyncWorkerMain and pg_sync_replication_slots the
> variable app_name.data is being used after it is freed.
>
> We can get logs as following:
> 2025-09-02 12:26:48.520 IST [3908359] ERROR:  synchronization worker
> "" could not connect to the primary server: connection to server at
> "localhost" (127.0.0.1), port 5432 failed: Connection refused
>         Is the server running on that host and accepting TCP/IP connections?
>
> I have moved the pfree(app_data.name) after its usage.
>
> This change was introduced in PG_18.
> The patch applies in the HEAD and REL_18_STABLE branches.
>

Thanks for the patch. It looks good to me. I'll take care of it.

-- 
With Regards,
Amit Kapila.

  3. Re: Fix use of variable after pfree

    Daniel Gustafsson <daniel@yesql.se> — 2025-09-02T08:56:26Z

    > On 2 Sep 2025, at 09:42, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Tue, Sep 2, 2025 at 1:02 PM Shlok Kyal <shlok.kyal.oss@gmail.com> wrote:

>> While going through the code of the slot sync worker, I found that in
>> functions ReplSlotSyncWorkerMain and pg_sync_replication_slots the
>> variable app_name.data is being used after it is freed.
>> 
>> We can get logs as following:
>> 2025-09-02 12:26:48.520 IST [3908359] ERROR:  synchronization worker
>> "" could not connect to the primary server: connection to server at
>> "localhost" (127.0.0.1), port 5432 failed: Connection refused
>>        Is the server running on that host and accepting TCP/IP connections?
>> 
>> I have moved the pfree(app_data.name) after its usage.
>> 
>> This change was introduced in PG_18.
>> The patch applies in the HEAD and REL_18_STABLE branches.
> 
> Thanks for the patch. It looks good to me. I'll take care of it.

Agreed, this looks correct.

--
Daniel Gustafsson