linux-kernel - Re: [PATCH 1/1] uprobes: Fix the memory out of bound overwrite in copy

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Date:	Wed, 13 Nov 2013 16:08:37 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	David Long <dave.long@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] uprobes: Fix the memory out of bound overwrite in
 copy_insn()

* Oleg Nesterov <oleg@...hat.com> [2013-11-07 20:40:32]:

> 1. copy_insn() doesn't look very nice, all calculations are
>    confusing and it is not immediately clear why do we read
>    the 2nd page first.
> 
> 2. The usage of inode->i_size is wrong on 32-bit machines.
> 
> 3. "Instruction at end of binary" logic is simply wrong, it
>    doesn't handle the case when uprobe->offset > inode->i_size.
> 
>    In this case "bytes" overflows, and __copy_insn() writes to
>    the memory outside of uprobe->arch.insn.
> 
>    Yes, uprobe_register() checks i_size_read(), but this file
>    can be truncated after that. All i_size checks are racy, we
>    do this only to catch the obvious mistakes.
> 
> Change copy_insn() to call __copy_insn() in a loop, simplify
> and fix the bytes/nbytes calculations.
> 
> Note: we do not care if offset + size > i_size, the users of
> arch_uprobe->insn can't know how many bytes were actually copied
> anyway. But perhaps this needs more changes.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju

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