[PATCH] ipc: fix to protect IPCS lookups using RCU

[Jeongjun Park <aha310510@gmail.com>]

In shm_destroy_orphaned(), we are not performing updates to the IPCS and are
only calling idr_for_each(), which can be protected by the RCU read-critical
section.

And if idr_for_each() is not protected by the RCU read-critical section,
then when radix_tree_node_free() is called to free the struct radix_tree_node
through call_rcu(), the node will be freed immediately, and when reading the
next node in radix_tree_for_each_slot(), the memory that has already been
freed may be read.

Therefore, when calling idr_for_each() in shm_destroy_orphaned(), it should
be modify to protect it within the RCU read critical section.

Reported-by: syzbot+a2b84e569d06ca3a949c@syzkaller.appspotmail.com
Fixes: b34a6b1da371 ("ipc: introduce shm_rmid_forced sysctl")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 ipc/shm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ipc/shm.c b/ipc/shm.c
index 99564c870084..baef5afadfb9 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -431,8 +431,10 @@ static int shm_try_destroy_orphaned(int id, void *p, void *data)
 void shm_destroy_orphaned(struct ipc_namespace *ns)
 {
 	down_write(&shm_ids(ns).rwsem);
+	rcu_read_lock();
 	if (shm_ids(ns).in_use)
 		idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
+	rcu_read_unlock();
 	up_write(&shm_ids(ns).rwsem);
 }
 
--