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[Bug 786208] Re: Missing checks for non-existent device in ide_exec_cmd

From: Thomas Huth
Subject: [Bug 786208] Re: Missing checks for non-existent device in ide_exec_cmd
Date: Thu, 12 Nov 2020 09:00:37 -0000

The QEMU project is currently considering to move its bug tracking to another 
system. For this we need to know which bugs are still valid and which could be 
closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state 
back to "New" within the next 60 days, otherwise this report will be marked as 
"Expired". Or mark it as "Fix Released" if the problem has been solved with a 
newer version of QEMU already. Thank you and sorry for the inconvenience.

** Changed in: qemu
     Assignee: John Snow (jnsnow) => (unassigned)

** Changed in: qemu
       Status: New => Incomplete

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  Missing checks for non-existent device in ide_exec_cmd

Status in QEMU:

Bug description:
  Several calls in the ide_exec_cmd handler are missing checks for
  (!s->bs) or similar, resulting in NULL pointer dereferences, divide-
  by-zero, or possibly other badness if the guest performs operations on
  a non-existent IDE master.

  For example, the WIN_READ_NATIVE_MAX command does a 'ide_set_sector(s,
  s->nb_sectors - 1);', which does 'cyl = sector_num / (s->heads *
  s->sectors);', which will fail with a divide-by-zero if heads =
  sectors = 0.

  And WIN_MULTREAD also does not check for s->bs, but does a
  'ide_sector_read(s);', which will do 'bdrv_read(s->bs, sector_num,
  s->io_buffer, n);' on a NULL s->bs, leading to a segfault.

  I do not *believe* that a malicious guest can do anything more than
  cause a crash with these bugs.

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