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From: | Alberto Garcia |
Subject: | Re: [Qemu-block] [PATCH 1/2] block: Detect multiplication overflow in bdrv_getlength |
Date: | Fri, 15 May 2015 10:04:04 +0200 |
User-agent: | Notmuch/0.13.2 (http://notmuchmail.org) Emacs/23.2.1 (i486-pc-linux-gnu) |
On Fri 15 May 2015 03:39:10 AM CEST, Fam Zheng <address@hidden> wrote: > int64_t ret = bdrv_nb_sectors(bs); > > + ret = (int64_t)(ret * BDRV_SECTOR_SIZE) < 0 ? -EFBIG : ret; > return ret < 0 ? ret : ret * BDRV_SECTOR_SIZE; Maybe in this case you're safe, but in general there's no guarantee that if there's an overflow the result will be negative. You can do something like this instead: ret = ret > INT64_MAX / BDRV_SECTOR_SIZE ? -EFBIG : ret; Of course this is only valid if BDRV_SECTOR_SIZE != 0 ;) Berto
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