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Re: [PATCH v2] hw/ide: check null block before _cancel_dma_sync

From: P J P
Subject: Re: [PATCH v2] hw/ide: check null block before _cancel_dma_sync
Date: Fri, 18 Sep 2020 15:55:52 +0530 (IST)

+-- On Fri, 18 Sep 2020, Li Qiang wrote --+
| Update v2: use an assert() call
|   ->https://lists.nongnu.org/archive/html/qemu-devel/2020-08/msg08336.html
| I think it is better to defer this check to 'ide_cancel_dma_sync'. 
| 'ide_cancel_dma_sync' is also called by 'cmd_device_reset' and all of the 
| handlers of 'ide_cmd_table' will check whether the 's->blk' is NULL in the 
| beginning of 'ide_exec_cmd'.
| So I think it is reasonable to check 's->blk' at the begining of 
| 'ide_cancel_dma_sync'.

* Yes, earlier patch v1 above does the same.

* From Peter's reply in another thread of similar issue I gather, issue is 
  setting 'blk' to NULL, even erroneously. So (blk == NULL) check should be 
  done where 'blk' is set to null, rather than where it is dereferenced.

* At the dereference point, assert(3) is good.

Thank you.
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

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