Replace the static error string in ZIP_Put_In_Cache0 with on stack memory (original) (raw)

Sean Chou zhouyx at linux.vnet.ibm.com
Wed Apr 18 03:15:19 UTC 2012

Hi David,

The current implementation uses static char array to keep the error

message, so it is possible when two errors happen at the same time, the error message will be modified. I have a testcase attached in http://mail.openjdk.java.net/pipermail/core-libs-dev/2012-April/009766.html .

So in the patch, the static char array is modified to on stack char

array to avoid the race in error case; and strdup is called because the error message is currently kept on stack. But I didn't notice the case that strdup might fail.

On Wed, Apr 18, 2012 at 10:43 AM, David Holmes <david.holmes at oracle.com>wrote:

Hi Sean,

On 18/04/2012 12:37 PM, Sean Chou wrote: To free the error string in ZIPOpen is a result of discussion with hotspot. They said the error string is never used and they do not want to do the free work in hotspot for ZIPOpen...

Ok. I assume there are no other callers of this method. strdup would cause a NULL error string if memory allocation is failed. If strdup is not used, another choice may be asking the caller to reserve the space for error string. Caller can reserve the space on stack, so *pmsg can still be set to NULL in ZIPPutInCache0 and caller can keep the code for error handling. But this is also strange. Do you have any better solutions? I'm still unclear why the strdup is being used on string literals. Are we concerned with someone modifying the contents of the string literals? It will not cause SEGV, there are NULL checks before free. It is not the free that I'm worried about. If an error occurs but the strdup fails due to a malloc failure then the caller may reference the msg. Previously this msg was never NULL but now it may be. David ----- On Tue, Apr 17, 2012 at 10:48 AM, David Holmes <david.holmes at oracle.com_ _<mailto:david.holmes at oracle.**com <david.holmes at oracle.com>>> wrote: Certainly the string management in this code is a bit of a mess, but I don't understand why the strdup's of string literals have been introduced. Even if for a good reason this seems to imply that an allocation failure will result in a NULL where before the caller was guaranteed never to get NULL in the error case, and that could lead to SEGV. Also with the change to avoid changes on the hotspot side, the actual cause of the open failure has been lost in ZIPOpen David

On 13/04/2012 1:14 AM, Sean Chou wrote: Hi Alan, I made a new webrev, added the comments and the 2 other modification. It's now : http://cr.openjdk.java.net/_**zhouyx/7159982/webrev.02/<http://cr.openjdk.java.net/_zhouyx/7159982/webrev.02/> <http://cr.openjdk.java.net/**zhouyx/7159982/webrev.02/<http://cr.openjdk.java.net/zhouyx/7159982/webrev.02/> > On Thu, Apr 12, 2012 at 4:24 PM, Alan Bateman<Alan.Bateman at oracle._**com_ _<mailto:Alan.Bateman at oracle.**com <Alan.Bateman at oracle.com> >>wrote: On 12/04/2012 06:40, Sean Chou wrote: Hi Alan, Many thanks. I updated the patch, ZIPOpen frees the error message and set "Zip file open error". The new webrev is : http://cr.openjdk.java.net/~** zhouyx/7159982/webrev.01/<**http_://cr.openjdk.java.net/%_ _**_7Ezhouyx/7159982/webrev.01/_ _<http://cr.openjdk.java.net/%**7Ezhouyx/7159982/webrev.01/<http://cr.openjdk.java.net/%7Ezhouyx/7159982/webrev.01/> >><_ _http://cr.openjdk.java.net/%****_ __7Ezhouyx/7159982/webrev.01/_ _<http://cr.openjdk.java.net/%***_ _*7Ezhouyx/7159982/webrev.01/><**ht_tp://cr.openjdk.java.net/%**_ __7Ezhouyx/7159982/webrev.01/_ _<http://cr.openjdk.java.net/%**7Ezhouyx/7159982/webrev.01/<http://cr.openjdk.java.net/%7Ezhouyx/7159982/webrev.01/> >>

Please take a look once more. This looks much better. I think we'll need to add comments to the ZIP* functions so that it's clear to anyone using them when they need to free the error message and then they don't. One implementation nit at ziputil.c L876 where it should check if pmsg is NULL and I think the tests should be reversed so that its: if (file != NULL&& pmsg != NULL&& *pmsg != NULL) { ... } One other minor nit is L875 where there is a space on either side of the "*", best to keep the style consistent. -Alan.

-- Best Regards, Sean Chou

-- Best Regards, Sean Chou

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