linux-kernel - [PATCH] x86/mce: Avoid using object after free in genpool.

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Date:	Wed, 23 Mar 2016 09:14:40 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	linux-kernel@...r.kernel.org,
	"Chen, Gong" <gong.chen@...ux.intel.com>
Subject: [PATCH] x86/mce: Avoid using object after free in genpool.

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@...r.kernel.org
Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 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));
-- 
2.5.0