Re: [PATCH] x86/mce: Avoid using object after free in genpool.

[Borislav Petkov]

On Wed, Mar 23, 2016 at 09:14:40AM -0700, Tony Luck wrote:
> When we loop over all queued machine check error records to pass
> them to the registered notifiers we use llist_for_each_entry().
> But the loop calls gen_pool_free() for the entry in the body of
> the loop - and then the iterator looks at node->next after the
> free.
> 
> Use llist_for_each_entry_safe() instead.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/mcheck/mce-genpool.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/mce-genpool.c b/arch/x86/kernel/cpu/mcheck/mce-genpool.c
> index 0a850100c594..2658e2af74ec 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce-genpool.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce-genpool.c
> @@ -29,7 +29,7 @@ static char gen_pool_buf[MCE_POOLSZ];
>  void mce_gen_pool_process(void)
>  {
>  	struct llist_node *head;
> -	struct mce_evt_llist *node;
> +	struct mce_evt_llist *node, *tmp;
>  	struct mce *mce;
>  
>  	head = llist_del_all(&mce_event_llist);
> @@ -37,7 +37,7 @@ void mce_gen_pool_process(void)
>  		return;
>  
>  	head = llist_reverse_order(head);
> -	llist_for_each_entry(node, head, llnode) {
> +	llist_for_each_entry_safe(node, tmp, head, llnode) {
>  		mce = &node->mce;
>  		atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce);
>  		gen_pool_free(mce_evt_pool, (unsigned long)node, sizeof(*node));
> -- 

Acked-by: Borislav Petkov <bp@xxxxxxx>

I have a couple more RAS patches for tip, want me to pick that one up
too? I'm going to send my pile to tip guys after -rc1 is out.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.