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From: Oliver Upton <oupton@google.com>
To: kvmarm@lists.cs.columbia.edu
Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Peter Shier <pshier@google.com>,
	Ricardo Koller <ricarkol@google.com>,
	Reiji Watanabe <reijiw@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Oliver Upton <oupton@google.com>,
	stable@kernel.org
Subject: [PATCH 2/4] KVM: Only log about debugfs directory collision once
Date: Sat,  2 Apr 2022 17:40:42 +0000	[thread overview]
Message-ID: <20220402174044.2263418-3-oupton@google.com> (raw)
In-Reply-To: <20220402174044.2263418-1-oupton@google.com>

In all likelihood, a debugfs directory name collision is the result of a
userspace bug. If userspace closes the VM fd without releasing all
references to said VM then the debugfs directory is never cleaned.

Even a ratelimited print statement can fill up dmesg, making it
particularly annoying for the person debugging what exactly went wrong.
Furthermore, a userspace that wants to be a nuisance could clog up the
logs by deliberately holding a VM reference after closing the VM fd.

Dial back logging to print at most once, given that userspace is most
likely to blame. Leave the statement in place for the small chance that
KVM actually got it wrong.

Cc: stable@kernel.org
Fixes: 85cd39af14f4 ("KVM: Do not leak memory for duplicate debugfs directories")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 69c318fdff61..38b30bd60f34 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -959,7 +959,7 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
 	mutex_lock(&kvm_debugfs_lock);
 	dent = debugfs_lookup(dir_name, kvm_debugfs_dir);
 	if (dent) {
-		pr_warn_ratelimited("KVM: debugfs: duplicate directory %s\n", dir_name);
+		pr_warn_once("KVM: debugfs: duplicate directory %s\n", dir_name);
 		dput(dent);
 		mutex_unlock(&kvm_debugfs_lock);
 		return 0;
-- 
2.35.1.1094.g7c7d902a7c-goog


WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oupton@google.com>
To: kvmarm@lists.cs.columbia.edu
Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	Peter Shier <pshier@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	stable@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: [PATCH 2/4] KVM: Only log about debugfs directory collision once
Date: Sat,  2 Apr 2022 17:40:42 +0000	[thread overview]
Message-ID: <20220402174044.2263418-3-oupton@google.com> (raw)
In-Reply-To: <20220402174044.2263418-1-oupton@google.com>

In all likelihood, a debugfs directory name collision is the result of a
userspace bug. If userspace closes the VM fd without releasing all
references to said VM then the debugfs directory is never cleaned.

Even a ratelimited print statement can fill up dmesg, making it
particularly annoying for the person debugging what exactly went wrong.
Furthermore, a userspace that wants to be a nuisance could clog up the
logs by deliberately holding a VM reference after closing the VM fd.

Dial back logging to print at most once, given that userspace is most
likely to blame. Leave the statement in place for the small chance that
KVM actually got it wrong.

Cc: stable@kernel.org
Fixes: 85cd39af14f4 ("KVM: Do not leak memory for duplicate debugfs directories")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 69c318fdff61..38b30bd60f34 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -959,7 +959,7 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
 	mutex_lock(&kvm_debugfs_lock);
 	dent = debugfs_lookup(dir_name, kvm_debugfs_dir);
 	if (dent) {
-		pr_warn_ratelimited("KVM: debugfs: duplicate directory %s\n", dir_name);
+		pr_warn_once("KVM: debugfs: duplicate directory %s\n", dir_name);
 		dput(dent);
 		mutex_unlock(&kvm_debugfs_lock);
 		return 0;
-- 
2.35.1.1094.g7c7d902a7c-goog

_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oupton@google.com>
To: kvmarm@lists.cs.columbia.edu
Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	James Morse <james.morse@arm.com>,
	 Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	 linux-arm-kernel@lists.infradead.org,
	Peter Shier <pshier@google.com>,
	 Ricardo Koller <ricarkol@google.com>,
	Reiji Watanabe <reijiw@google.com>,
	 Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	 Oliver Upton <oupton@google.com>,
	stable@kernel.org
Subject: [PATCH 2/4] KVM: Only log about debugfs directory collision once
Date: Sat,  2 Apr 2022 17:40:42 +0000	[thread overview]
Message-ID: <20220402174044.2263418-3-oupton@google.com> (raw)
In-Reply-To: <20220402174044.2263418-1-oupton@google.com>

In all likelihood, a debugfs directory name collision is the result of a
userspace bug. If userspace closes the VM fd without releasing all
references to said VM then the debugfs directory is never cleaned.

Even a ratelimited print statement can fill up dmesg, making it
particularly annoying for the person debugging what exactly went wrong.
Furthermore, a userspace that wants to be a nuisance could clog up the
logs by deliberately holding a VM reference after closing the VM fd.

Dial back logging to print at most once, given that userspace is most
likely to blame. Leave the statement in place for the small chance that
KVM actually got it wrong.

Cc: stable@kernel.org
Fixes: 85cd39af14f4 ("KVM: Do not leak memory for duplicate debugfs directories")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 69c318fdff61..38b30bd60f34 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -959,7 +959,7 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
 	mutex_lock(&kvm_debugfs_lock);
 	dent = debugfs_lookup(dir_name, kvm_debugfs_dir);
 	if (dent) {
-		pr_warn_ratelimited("KVM: debugfs: duplicate directory %s\n", dir_name);
+		pr_warn_once("KVM: debugfs: duplicate directory %s\n", dir_name);
 		dput(dent);
 		mutex_unlock(&kvm_debugfs_lock);
 		return 0;
-- 
2.35.1.1094.g7c7d902a7c-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2022-04-02 17:40 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-02 17:40 [PATCH 0/4] KVM: arm64: Fix use-after-free in debugfs Oliver Upton
2022-04-02 17:40 ` Oliver Upton
2022-04-02 17:40 ` Oliver Upton
2022-04-02 17:40 ` [PATCH 1/4] KVM: arm64: vgic: Don't assume the VM debugfs directory exists Oliver Upton
2022-04-02 17:40   ` Oliver Upton
2022-04-02 17:40   ` Oliver Upton
2022-04-02 22:39   ` Oliver Upton
2022-04-02 22:39     ` Oliver Upton
2022-04-02 22:39     ` Oliver Upton
2022-04-02 17:40 ` Oliver Upton [this message]
2022-04-02 17:40   ` [PATCH 2/4] KVM: Only log about debugfs directory collision once Oliver Upton
2022-04-02 17:40   ` Oliver Upton
2022-04-04 17:33   ` Sean Christopherson
2022-04-04 17:33     ` Sean Christopherson
2022-04-04 17:33     ` Sean Christopherson
2022-04-04 17:57     ` Oliver Upton
2022-04-04 17:57       ` Oliver Upton
2022-04-04 17:57       ` Oliver Upton
2022-04-02 17:40 ` [PATCH 3/4] selftests: KVM: Don't leak GIC FD across dirty log test iterations Oliver Upton
2022-04-02 17:40   ` Oliver Upton
2022-04-02 17:40   ` Oliver Upton
2022-04-02 19:26   ` Jing Zhang
2022-04-02 19:26     ` Jing Zhang
2022-04-02 19:26     ` Jing Zhang
2022-04-02 17:40 ` [PATCH 4/4] selftests: KVM: Free the GIC FD when cleaning up in arch_timer Oliver Upton
2022-04-02 17:40   ` Oliver Upton
2022-04-02 17:40   ` Oliver Upton

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