JDK-8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true #2995

tstuefe · 2021-03-14T06:09:26Z

Sonarcloud reports a possible NULL dereference when zapping the to-be-freed area in fast-path arena free. Possible call stack for this to happen starts in Node::destruct(PhaseValues* phase).

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Issue

JDK-8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true

Reviewers

Kim Barrett (@kimbarrett - Reviewer)
Coleen Phillimore (@coleenp - Reviewer) ⚠️ Review applies to ceaef85

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bridgekeeper · 2021-03-14T06:09:52Z

👋 Welcome back stuefe! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2021-03-14T06:10:52Z

@tstuefe The following label will be automatically applied to this pull request:

hotspot-runtime

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2021-03-14T08:49:21Z

Webrevs

kimbarrett · 2021-03-14T19:21:39Z

src/hotspot/share/memory/arena.hpp

@@ -185,7 +185,9 @@ class Arena : public CHeapObj<mtNone> {
  // Fast delete in area.  Common case is: NOP (except for storage reclaimed)
  bool Afree(void *ptr, size_t size) {
 #ifdef ASSERT
-    if (ZapResourceArea) memset(ptr, badResourceValue, size); // zap freed memory
+    if (ZapResourceArea && ptr != NULL) {


The pointer arithmetic on line 193 is UB if ptr is nullptr (though it's unlikely anyone checks), so either Afree has ptr != nullptr as an (unstated) precondition or there are potentially more problems than the memset.

tstuefe · 2021-03-15T05:53:57Z

Thanks Kim. I changed the fix to fix the one caller I was sure about passing NULL, and assert in AFree instead.

(update: looking at Node::destruct, I believe the coding was correct and there is no way this could have been called with NULL; so I reduce this patch to just the assert in AFree)

I removed the Trivial mark. Before pushing I will put this through tests to check if it triggers. I believe even though the pointer arithmetic below was UB with NULL, the effect would have in general been benign (just refusing to free anything).

openjdk · 2021-03-15T06:49:29Z

@tstuefe This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true

Reviewed-by: kbarrett, coleenp

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 114 new commits pushed to the master branch:

5b8233b: 8263871: On sem_destroy() failing we should assert
96e5c3f: 8263890: Broken links to Unicode.org
4d9517d: 8263834: Work around gdb for HashtableEntry
6fa6557: 8263825: Remove unused and commented out member from NTLMException
77ebc11: 8263892: More modifier order fixes in java.base
80d3ea0: 8263885: Use the blessed modifier order in java.sql/rowset/transation.xa
6737135: 8262083: vmTestbase/nsk/jvmti/SetEventNotificationMode/setnotif001/TestDescription.java failed with "No notification: event JVMTI_EVENT_FRAME_POP (61)"
57fc8e9: 8262080: vmTestbase/nsk/jdi/Event/request/request001/TestDescription.java failed with "ERROR: new event is not ThreadStartEvent"
0b5216a: 8263545: Convert jpackage to use Stream.toList()
ed701ea: 8262271: SA: Add new stress test that tests getting the stack trace of an active thread
... and 104 more: https://git.openjdk.java.net/jdk/compare/9c84899da4689b395d0089e6cb777cb50cd3e547...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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mlbridge · 2021-03-15T06:50:08Z

Mailing list message from Kim Barrett on hotspot-runtime-dev:

On Mar 15, 2021, at 1:59 AM, Thomas Stuefe <stuefe at openjdk.java.net> wrote:

On Sun, 14 Mar 2021 06:09:26 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

Sonarcloud reports a possible NULL dereference when zapping the to-be-freed area in fast-path arena free. Possible call stack for this to happen starts in Node::destruct(PhaseValues* phase).

Thanks Kim. I changed the fix to fix the one caller I was sure about passing NULL, and assert in AFree instead.

(The skara bots don?t resend edited comments, so this is missing your update, quoted below.)

(update: looking at Node::destruct, I believe the coding was correct and there is no way this could have been called with NULL; so I reduce this patch to just the assert in AFree)

I looked at it too, and agree with your assessment.

I removed the Trivial mark. Before pushing I will put this through tests to check if it triggers. I believe even though the pointer arithmetic below was UB with NULL, the effect would have in general been benign (just refusing to free anything).

I also agree the UB won?t be detected and the effect benign.

Looks good.

tstuefe · 2021-03-15T06:58:56Z

Mailing list message from Kim Barrett on hotspot-runtime-dev:

Looks good.

Thanks Kim.

coleenp

Looks good.

tstuefe · 2021-03-16T05:54:02Z

Thanks @coleenp and @kimbarrett . However, as I feared, with the assert alone I now see it firing both in our nightlies at SAP and in the GAs in compiler tests.

Which is cool in a way since this is the first time SonarCloud reported anything demonstrably real.:) I'll take a look at the crashes and modify the patch.

tstuefe · 2021-03-16T07:03:02Z

I changed the patch to provide the same semantics on passed old ptr == NULL as standard free(3) and realloc(3) have. Which is to ignore it (free) or to revert to malloc (realloc).

The culprit in this case - calling realloc with a NULL pointer - was aot, ImplicitExceptionTable::append( uint exec_off, uint cont_off ).

I considered fixing the caller, but I am used to the C-runtime semantics in free and realloc, and it looks like others are too; so this is the least surprising behavior for a realloc-like function.

Also, this fixes the subtle bug where, when passing NULL to Arealloc, we would return "false" to indicate that we have a lossfull realloc. The only case I can see where the return value was actually used was in SymbolTable::delete_symbol() which would print something about leaked symbols in that case. I did not investigate whether this has any practical relevance.

tstuefe · 2021-03-17T05:26:29Z

Coleen, Kim, are you fine with this latest version? Thanks!

kimbarrett · 2021-03-18T00:10:23Z

src/hotspot/share/memory/arena.cpp

@@ -366,6 +366,10 @@ void* Arena::grow(size_t x, AllocFailType alloc_failmode) {
 // Reallocate storage in Arena.
 void *Arena::Arealloc(void* old_ptr, size_t old_size, size_t new_size, AllocFailType alloc_failmode) {
  if (new_size == 0) return NULL;


[pre-existing] Isn't this a leak? Probably just dropping old_ptr.

Yes, it is a leak, at least if we run with UseMallocOnly. I think this, and Amalloc, should behave consistently with os::malloc here, which is to return a small non-null allocation for size=0. Basically, if size==0 size=1.

src/hotspot/share/memory/arena.cpp

kimbarrett

Looks good.

tstuefe · 2021-03-20T09:06:12Z

Thanks Coleen & Kim!

/integrate

openjdk · 2021-03-20T09:07:31Z

@tstuefe Since your change was applied there have been 115 commits pushed to the master branch:

ab66d69: 8263138: Initialization of sun.font.SunFontManager.platformFontMap is not thread safe
5b8233b: 8263871: On sem_destroy() failing we should assert
96e5c3f: 8263890: Broken links to Unicode.org
4d9517d: 8263834: Work around gdb for HashtableEntry
6fa6557: 8263825: Remove unused and commented out member from NTLMException
77ebc11: 8263892: More modifier order fixes in java.base
80d3ea0: 8263885: Use the blessed modifier order in java.sql/rowset/transation.xa
6737135: 8262083: vmTestbase/nsk/jvmti/SetEventNotificationMode/setnotif001/TestDescription.java failed with "No notification: event JVMTI_EVENT_FRAME_POP (61)"
57fc8e9: 8262080: vmTestbase/nsk/jdi/Event/request/request001/TestDescription.java failed with "ERROR: new event is not ThreadStartEvent"
0b5216a: 8263545: Convert jpackage to use Stream.toList()
... and 105 more: https://git.openjdk.java.net/jdk/compare/9c84899da4689b395d0089e6cb777cb50cd3e547...master

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start

8181b61

openjdk bot added the hotspot-runtime label Mar 14, 2021

tstuefe marked this pull request as ready for review Mar 14, 2021

openjdk bot added the rfr label Mar 14, 2021

kimbarrett reviewed Mar 14, 2021

View changes

move check to caller; assert in AFree instead

aab8bbf

tstuefe added 2 commits Mar 15, 2021

reduce diff

bcbe6cd

just the assert

ceaef85

kimbarrett approved these changes Mar 15, 2021

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openjdk bot added the ready label Mar 15, 2021

coleenp approved these changes Mar 15, 2021

View changes

make Arealloc and Afree behave like realloc and free

21a9494

kimbarrett suggested changes Mar 18, 2021

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Fix minor leak on Arealloc if new_size is 0

d401e3c

kimbarrett approved these changes Mar 20, 2021

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openjdk bot closed this Mar 20, 2021

openjdk bot added integrated and removed ready rfr labels Mar 20, 2021

tstuefe deleted the JDK-8263558-Arena-afree-null-deref branch Apr 26, 2021

openjdk / jdk Public

JDK-8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true #2995

JDK-8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true #2995

tstuefe commented Mar 14, 2021 •

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JDK-8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true #2995

JDK-8263558: Possible NULL dereference in fast path arena free if ZapResourceArea is true #2995

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