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Re: [libvirt] [PATCH] qemu: Fix crash on failed VM startup

Eric Blake wrote:
On 06/01/2010 01:10 PM, Cole Robinson wrote:
If VM startup fails early enough (can't find a referenced USB device),
libvirtd will crash trying to clear the VNC port bit, since port = 0,
which overflows us out of the bitmap bounds.

Fix this by being more defensive in the bitmap operations, and only
clearing a previously set VNC port.

+++ b/src/util/bitmap.c
@@ -118,7 +118,7 @@ int virBitmapSetBit(virBitmapPtr bitmap, size_t b)
 int virBitmapClearBit(virBitmapPtr bitmap, size_t b)
-    if (b > bitmap->size - 1)
+    if (bitmap->size != 0 && b > bitmap->size - 1)

I think this could use a v2: virBitmapSetBit and virBitmapGetBit should
get the same treatment for bounds checking.

Meanwhile, we already reject attempts to create a bitmap with SIZE_MAX
bits.  Therefore, since b is unsigned, we can safely avoid the && and
instead do the computation via a single comparison:

if (bitmap->size <= b)
    return -1;

For that matter, should virBitmapAlloc(0) return NULL, instead of it's
current behavior of allocating an (empty) bitmap?

Yes, you are right - especially since there is no grow operation :-). I should have returned NULL for size 0 request in the original version.


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