Fix a potential Use-after-free in test_blockjob_common_drain_node() (v6.2.0).

[wliang]

Hi all,

I find a potential Use-after-free in QEMU 6.2.0, which is in test_blockjob_common_drain_node() (./tests/unit/test-bdrv-drain.c).

Specifically, at line 880, the variable 'scr' is released by the bdrv_unref(). However, at line 881, it is subsequently used as the 1st parameter of the function bdrv_set_backing_hd(). As a result, an UAF bug may be triggered.

880     bdrv_unref(src);

881     bdrv_set_backing_hd(src, src_backing, &error_abort);

I believe that the problem can be fixed by invoking bdrv_unref() after the call of bdrv_set_backing_hd() rather than before it.


---     bdrv_unref(src);
881     bdrv_set_backing_hd(src, src_backing, &error_abort);
+++ bdrv_unref(src);


I'm looking forward to your confirmation.

Best,
Wentao

test-bdrv-drain.patch
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