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Re: [PATCH] Make strlen range computations more conservative


On 07/31/2018 12:38 AM, Jakub Jelinek wrote:
On Mon, Jul 30, 2018 at 09:45:49PM -0600, Martin Sebor wrote:
Even without _FORTIFY_SOURCE GCC diagnoses (some) writes past
the end of subobjects by string functions.  With _FORTIFY_SOURCE=2
it calls abort.  This is the default on popular distributions,

Note that _FORTIFY_SOURCE=2 is the mode that goes beyond what the standard
requires, imposes extra requirements.  So from what this mode accepts or
rejects we shouldn't determine what is or isn't considered valid.

I'm not sure what the additional requirements are but the ones
I am referring to are the enforcing of struct member boundaries.
This is in line with the standard requirements of not accessing
[sub]objects via pointers derived from other [sub]objects.

The one area where Builtin Object Size doesn't faithfully reflect
subobject boundaries is arrays of of arrays.  This was a serious
concern for the security group at my last company (see bug 44384)
We developed (proprietary) patches to mitigate the shortcoming.

Martin


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