Re: RFR: 8049695: nsk/jdb/options/connect/connect003 fails with "Launched jdb could not attach to debuggee during 300000 milliseconds"

[Alex Menkov]

Updated fix:
http://cr.openjdk.java.net/~amenkov/shmem_long_name/webrev_open.02/

The changes:
- createTransport function is fixed;
- "prefix" variable is renamed to "baseName".

--alex

On 03/14/2018 09:45, Alex Menkov wrote:

Hi David,


On 03/13/2018 17:46, David Holmes wrote:

Hi Alex,

On 14/03/2018 9:14 AM, Alex Menkov wrote:

Hi all,

Please review a small fix for
https://bugs.openjdk.java.net/browse/JDK-8049695
webrev: http://cr.openjdk.java.net/~amenkov/shmem_long_name/webrev_open/

Root cause of the issue is jbd hungs as a result of the buffer overflow.

In the beginning of the shmemBase.c:

#define MAX_IPC_PREFIX 50   /* user-specified or generated name for */

                             /* shared memory seg and prefix for other IPC */ #define MAX_IPC_SUFFIX 25   /* suffix to shmem name for other IPC names */

#define MAX_IPC_NAME   (MAX_IPC_PREFIX + MAX_IPC_SUFFIX)

buffer (char prefix[]) in function createStream is used to generate base name for mutex/events, so MAX_IPC_PREFIX is not big enough.

Good catch! But overall this code seems to be missing bounds checks everywhere. You made the "prefix" (poor name?) buffer bigger (MAX_IPC_NAME) but do we know the incoming name plus the appended descriptive string will fit in it?

Yes, the possible values can be added to the shmem name (which is restricted by 49 chars):

".mutex"
".hasData"
".hasSpace"
".accept"
".attach"
".<pid>" (pid is 64bit value, max len IIRC is 19 symbols)
So extra MAX_IPC_SUFFIX (25 symbols) is enough

Looking at createTransport for example, it also has:

char prefix[MAX_IPC_PREFIX];

and it produces an error if

strlen(address) >= MAX_IPC_PREFIX

but otherwise copies it across:

strcpy(transport->name, address);

and then later does:

  sprintf(prefix, "%s.mutex", transport->name);

so we may have overflowed again by adding ".mutex"! The same goes for the subsequent sprintf's.

Thank you for the catch!

I looked the file for other similar issues, but somehow overlokked this case.

Will fix it.
Also will change confusing "prefix" name to "base_name".

--alex

So I think there is more work to do to ensure this code is immune from buffer overflows.

Thanks,
David
-----

--alex