[PATCH 4.4 003/163] x86/mce: Avoid using object after free in genpool

From: Greg Kroah-Hartman
Date: Mon May 02 2016 - 21:48:10 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Tony Luck <tony.luck@xxxxxxxxx>

commit a3125494cff084b098c80bb36fbe2061ffed9d52 upstream.

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.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Gong Chen <gong.chen@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-edac <linux-edac@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/0205920@xxxxxxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1459929916-12852-4-git-send-email-bp@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/x86/kernel/cpu/mcheck/mce-genpool.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- 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)

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));