freebsd security - Jul 2011 - Malloc -Z

Was reading malloc(3) while chasing corruption suspects.
Does the presence of -Z imply that without it, programs
can be allocated dirty (non-zeroed) memory?
If so, it seems running with -Z would be prudent if one cares.
Therefore, what is the rough percent performance
impact of -Z compared to default malloc?

Bonus:
What would be needed to make the useful streams:
/dev/one
/dev/10
/dev/01
In addition to /dev/zero.

On 27/07/2011, at 4:49 PM, grarpamp wrote:
> Was reading malloc(3) while chasing corruption suspects.
> Does the presence of -Z imply that without it, programs
> can be allocated dirty (non-zeroed) memory?
> If so, it seems running with -Z would be prudent if one cares.
> Therefore, what is the rough percent performance
> impact of -Z compared to default malloc?
> 
malloc(3) has never provided zeroed memory. If you need zeroed memory in C, you
either need to zero it yourself using memset(3), or use calloc(3).

It's been part of the language standard for over 20 years now, and is the
same in that regard on every platform that provides malloc(3).

What would be prudent as a developer (and is the default in CURRENT I believe)
is to use J - it enforces the "memory from malloc(3) is not guaranteed to
be zeroed." by specifically setting it to non-zero.

> Bonus:
> What would be needed to make the useful streams:
> /dev/one
> /dev/10
> /dev/01
> In addition to /dev/zero.
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On Wed, 27 Jul 2011 02:49:48 -0400
grarpamp wrote:
> Was reading malloc(3) while chasing corruption suspects.
> Does the presence of -Z imply that without it, programs
> can be allocated dirty (non-zeroed) memory?
Programs (in the sense of processes) are allocated zeroed-memory.

Memory allocated by malloc will either be zeroed or contain pages
written to by the same process. 

In general any security concerns about sensitive data should be handled
by zeroing before freeing (or when the data is no longer needed) rather
than zeroing on allocation.