locking/rwsem: Don't call owner_on_cpu() on read-owner
authorWaiman Long <longman@redhat.com>
Sat, 20 Jul 2019 15:04:10 +0000 (11:04 -0400)
committerIngo Molnar <mingo@kernel.org>
Thu, 25 Jul 2019 13:39:22 +0000 (15:39 +0200)
For writer, the owner value is cleared on unlock. For reader, it is
left intact on unlock for providing better debugging aid on crash dump
and the unlock of one reader may not mean the lock is free.

As a result, the owner_on_cpu() shouldn't be used on read-owner
as the task pointer value may not be valid and it might have
been freed. That is the case in rwsem_spin_on_owner(), but not in
rwsem_can_spin_on_owner(). This can lead to use-after-free error from
KASAN. For example,

  BUG: KASAN: use-after-free in rwsem_down_write_slowpath
  (/home/miguel/kernel/linux/kernel/locking/rwsem.c:669
  /home/miguel/kernel/linux/kernel/locking/rwsem.c:1125)

Fix this by checking for RWSEM_READER_OWNED flag before calling
owner_on_cpu().

Reported-by: Luis Henriques <lhenriques@suse.com>
Tested-by: Luis Henriques <lhenriques@suse.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Fixes: 94a9717b3c40e ("locking/rwsem: Make rwsem->owner an atomic_long_t")
Link: https://lkml.kernel.org/r/81e82d5b-5074-77e8-7204-28479bbe0df0@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/locking/rwsem.c

index 37524a4..bc91aac 100644 (file)
@@ -666,7 +666,11 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
        preempt_disable();
        rcu_read_lock();
        owner = rwsem_owner_flags(sem, &flags);
-       if ((flags & nonspinnable) || (owner && !owner_on_cpu(owner)))
+       /*
+        * Don't check the read-owner as the entry may be stale.
+        */
+       if ((flags & nonspinnable) ||
+           (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
                ret = false;
        rcu_read_unlock();
        preempt_enable();