linux-kernel - [PATCH] kvm: fix incorrect NULL check on list iterator

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Message-Id: <20220327051646.1856-1-xiam0nd.tong@gmail.com>
Date:   Sun, 27 Mar 2022 13:16:46 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     mpe@...erman.id.au
Cc:     benh@...nel.crashing.org, paulus@...ba.org,
        akpm@...ux-foundation.org, liam.howlett@...cle.com,
        david@...hat.com, maz@...nel.org, Felix.Kuehling@....com,
        maciej.szmigiero@...cle.com, apopple@...dia.com,
        bharata@...ux.ibm.com, linuxram@...ibm.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Xiaomeng Tong <xiam0nd.tong@...il.com>, stable@...r.kernel.org
Subject: [PATCH] kvm: fix incorrect NULL check on list iterator

The bug is here:
	if (!p)
                return ret;

The list iterator value 'p' will *always* be set and non-NULL by
list_for_each_entry(), so it is incorrect to assume that the iterator
value will be NULL if the list is empty or no element is found.

To fix the bug, Use a new value 'iter' as the list iterator, while use
the old value 'p' as a dedicated variable to point to the found element.

Cc: stable@...r.kernel.org
Fixes: dfaa973ae9605 ("KVM: PPC: Book3S HV: In H_SVM_INIT_DONE, migrate remaining normal-GFNs to secure-GFNs")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
 arch/powerpc/kvm/book3s_hv_uvmem.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index e414ca44839f..0cb20ee6a632 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -360,13 +360,15 @@ static bool kvmppc_gfn_is_uvmem_pfn(unsigned long gfn, struct kvm *kvm,
 static bool kvmppc_next_nontransitioned_gfn(const struct kvm_memory_slot *memslot,
 		struct kvm *kvm, unsigned long *gfn)
 {
-	struct kvmppc_uvmem_slot *p;
+	struct kvmppc_uvmem_slot *p = NULL, *iter;
 	bool ret = false;
 	unsigned long i;
 
-	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list)
-		if (*gfn >= p->base_pfn && *gfn < p->base_pfn + p->nr_pfns)
+	list_for_each_entry(iter, &kvm->arch.uvmem_pfns, list)
+		if (*gfn >= iter->base_pfn && *gfn < iter->base_pfn + iter->nr_pfns) {
+			p = iter;
 			break;
+		}
 	if (!p)
 		return ret;
 	/*
-- 
2.17.1