On Tue, Jun 16, 2020 at 08:42:08AM +0200, Michal Hocko wrote:

On Mon 15-06-20 21:57:16, Waiman Long wrote:

quoted

The kzfree() function is normally used to clear some sensitive
information, like encryption keys, in the buffer before freeing it back
to the pool. Memset() is currently used for the buffer clearing. However,
it is entirely possible that the compiler may choose to optimize away the
memory clearing especially if LTO is being used. To make sure that this
optimization will not happen, memzero_explicit(), which is introduced
in v3.18, is now used in kzfree() to do the clearing.

Fixes: 3ef0e5ba4673 ("slab: introduce kzfree()")
Cc: stable@vger.kernel.org
Signed-off-by: Waiman Long <longman@redhat.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Although I am not really sure this is a stable material. Is there any
known instance where the memset was optimized out from kzfree?

I told him to add the stable.  Otherwise it will just get reported to
me again.  It's a just safer to backport it before we forget.

regards,
dan carpenter


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