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Re: [libvirt] [PATCH] conf: Remove console stream callback only when freeing console helper



On 08/03/2012 05:27 PM, Peter Krempa wrote:
Commit ba226d334acbc49f6751b430e0c4e00f69eef6bf tried to fix crash of
the daemon when a domain with a open console was destroyed. The fix was
wrong as it tried to remove the callback also when the stream was
aborted, where at that point the fd stream driver was already freed and
removed.

This patch clears the callbacks with a helper right before the hash is
freed, so that it doesn't interfere with other codepaths where the
stream object is freed.

I just tried your patch, it still exists use after free issue:

==21843== 1 errors in context 1 of 11:
==21843== Invalid read of size 4
==21843==    at 0x4D2B79D: virStreamFree (libvirt.c:15345)
==21843==    by 0x40B2E1: vshRunConsole (console.c:404)
==21843==    by 0x4226CE: cmdRunConsole (virsh-domain.c:1658)
==21843==    by 0x422AE3: cmdConsole (virsh-domain.c:1693)
==21843==    by 0x42CBC4: vshCommandRun (virsh.c:1867)
==21843==    by 0x42F872: main (virsh.c:3269)
==21843==  Address 0x53c0250 is 0 bytes inside a block of size 40 free'd
==21843==    at 0x4A0595D: free (vg_replace_malloc.c:366)
==21843==    by 0x4C916C8: virFree (memory.c:309)
==21843==    by 0x4D111BB: virUnrefStream (datatypes.c:1072)
==21843==    by 0x4D2B7BD: virStreamFree (libvirt.c:15353)
==21843==    by 0x40A984: virConsoleShutdown (console.c:103)
==21843==    by 0x4C8912E: virEventPollRunOnce (event_poll.c:485)
==21843==    by 0x4C87CA4: virEventRunDefaultImpl (event.c:247)
==21843==    by 0x42C8A1: vshEventLoop (virsh.c:2406)
==21843==    by 0x4C9C065: virThreadHelper (threads-pthread.c:161)
==21843==    by 0x39CF8077F0: start_thread (pthread_create.c:301)
==21843==    by 0x39CF0E570C: clone (clone.S:115)


Regards,
Alex

---
  src/conf/virconsole.c |   16 +++++++++++++---
  1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/conf/virconsole.c b/src/conf/virconsole.c
index 912aff6..b3f6eb6 100644
--- a/src/conf/virconsole.c
+++ b/src/conf/virconsole.c
@@ -219,9 +219,6 @@ static void virConsoleHashEntryFree(void *data,
      const char *pty = name;
      virStreamPtr st = data;

-    /* remove callback from stream */
-    virFDStreamSetInternalCloseCb(st, NULL, NULL, NULL);
-
      /* free stream reference */
      virStreamFree(st);

@@ -290,6 +287,18 @@ error:
  }

  /**
+ * Helper to clear stream callbacks when freeing the hash
+ */
+static void virConsoleFreeClearCallbacks(void *payload,
+                                         const void *name ATTRIBUTE_UNUSED,
+                                         void *data ATTRIBUTE_UNUSED)
+{
+    virStreamPtr st = payload;
+
+    virFDStreamSetInternalCloseCb(st, NULL, NULL, NULL);
+}
+
+/**
   * Free structures for handling open console streams.
   *
   * @cons Pointer to the private structure.
@@ -300,6 +309,7 @@ void virConsoleFree(virConsolesPtr cons)
          return;

      virMutexLock(&cons->lock);
+    virHashForEach(cons->hash, virConsoleFreeClearCallbacks, NULL);
      virHashFree(cons->hash);
      virMutexUnlock(&cons->lock);
      virMutexDestroy(&cons->lock);


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