BUG #14930: Unchecked AllocateDir() return value in SlruScanDirectory()

The following bug has been logged on the website:

Bug reference: 14930
Logged by: Pan Bian
Email address: bianpan2016@163.com
PostgreSQL version: 10.1
Operating system: Linux
Description:

File: src/backend/access/transam/slru.c
Function: SlruScanDirectory
Line: 1385

AllocateDir() will return a NULL pointer if it fails to open the specified
directory. However, in function SlruScanDirectory(), its return value is not
checked. This may result in a NULL pointer dereference when trying to free
it (see line 1405).

For your convenience, I copy and paste related codes as follows:

1376 bool
1377 SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
1378 {
1379 bool retval = false;
1380 DIR *cldir;
1381 struct dirent *clde;
1382 int segno;
1383 int segpage;
1384
1385 cldir = AllocateDir(ctl->Dir);
...
1405 FreeDir(cldir);
1406
1407 return retval;
1408 }

Thank you!

Pan Bian